NEWNES PRACTICAL MECHANICS - WorldRadioHistory.Com...December, 1953 NEWNES PRACTICAL MECHANICS 103...

December, 19 53 NEWNES PRACTICAL MECHANICS 101

DECEMBER,1953

VOL. XXINo. 240

PRACTICALMECHANICS

The " Cyclist," "Practical Motorist," and "Home Movies" are temporarily incorporated.

FAIR COMMENT

More About Flying SaucersSINCE last month, when I commented

upon the recently published book" Flying Saucers Have Landed,"

which asserts that space ships had landed,That one of the occupants had beeninterviewed, and that several peoplewere witnesses of the particular incidentwhich is the subject of the book, one ofthe joint authors, Mr. Desmond Leslie,appeared in one of the television pro-grammes and amplified the matter.The B.B.C. has been inundated withtelephone calls and letters, and it is notsui prising that world-wide interest hasbeen evoked in what has become thegreatest scientific mystery of the presentcentury.

The book to which I referred includesphotographs of the ship used by theVenusian and also contains affidavits,sworn before notaries public, by thosewho were present at the time. Whetherone views the book with the eye of asceptic or accepts it as fact, there can beno doubt that mysterious objects havebeen seen in the sky by accreditedscientific people over a long period ofyears. It is just possible that the so-calledflying saucers are experimental crafton the secrets list, in spite of the denialsissued by the American Government.The most authentic stories relating toflying saucers have come from America.

The matter has been taken sufficientlyseriously in this country, especially afterMr. Leslie's broadcast, for questions tobe asked in Parliament, but it seemsunlikely that the Government knowsany more than has appeared in the Pressand in books. The matter cannotbe dismissed lightly for if, as is asserted,people from other planets have landed onthis earth it is a matter of importancenot only to the Government but toscientists. Many interesting questionsarise, not the least of which is whethersuch planetary visitors would be regardedas invaders, arrested, and their craftconfiscated for examination ?

Flying Saucers Through theCenturies

THE stories concerning flying saucersare too numerous and persistent for

the subject to be dismissed as a hoax and,indeed, through the centuries there havebeen reports of similar visitations. As

long ago as 1619 a long, fiery object wasseen flying in Switzerland ; a similarobject was seen over Worcester in 1661,and there have been similar reports in1704 (England), 1731 (Italy), 175o(Edinburgh), 1752 (Norway), 1755(Portugal), 1761 (Switzerland), 1777(France), 1802 (Germany), 1808(Piedmont), 1813 (Tottenham), 1816(Portugal), 1817 (Italy), 1818 (Ipswich),182o (France), 1821 (English Channel),1826 (France), and so on, up to thepresent time. Practically every yearfrom the middle of the 17th century havecome reports of strange objects seen inthe sky which have never been accountedfor. It is inconceivable that all of theseobservers, large numbers of them skilledastronomers and scientists, were sufferingfrom hallucinations. We must, therefore,acknowledge the existence of somemysterious craft which has only oneof two explanations. Flying saucersare either secret weapons, or they arespaceships from other planets.

Are Other Planets Inhabited ?THEORETICALLY, there is no reason

to suppose that other planets areuninhabited, nor that the inhabitantsare less scientific than we are. There isno scientific reason why the inquisitivescientific mind of those on other planetsshould not seek to explore the earth evenas we seek to travel some day to the Moon,to Venus, and to Mars. It seems reason-ably certain that experimental flights tothe Moon will be attempted before thiscentury has closed.

For this reason I propose next monthto review the book in greater detail andto include some of the photographs

SUBSCRIPTION RATESincluding postage for one year

Inland - - - - I4s. per annum.Abroad - - - - I4s. per annum.Editorial and Advertisement Office : " Practical

Mechanics," George Newnes, Ltd.,Tower House. Southampton Street, Strand, W.C.2

'Phone : Temple Bar 4363Telegrams : Newnes, Rand, London.

Copyright in all drawings, photographs andarticles published in " Practical MechUnics" isspecially reserved throughout the countriessignatory to the Berne Convention and theU.S.A. Reproductions or imitations of any of

these are therefore expressly forbidden.

- EDITOR

F. J. CAMM

By The Editor

which the authors have used to supporttheir report.

The Late W. J. Bassett-Lowke

IT is with deep regret that I report thepassing in the latter part of October

of Mr. W. J. Bassett-Lowke, a frequentcontributor to these pages over a longperiod of years, and the founder of themodel firm which bears his name. Itwould be true to say that he foundedthe model industry in this country, andwas the first to draw attention to theeducational value of realistic scale models.When he founded his firm over 5o yearsago there was no cinema, radio ortelevision. Youth depended to a greatextent upon practical crafts to occupytheir leisure time. Great interest inthose years was evinced in model railwaysalthough to -day interest in that particularhobby is much less marked owing tothe competition of radio and television,model aircraft and model boats. Not-withstanding this competition, Lowkerefused to enter the model aircraftfield and remained faithful to modelrailways and model boats. His businessexpanded from Northampton to Londonand Manchester, and the windows ofmany shipping companies display therealism which was built into his models.

In spite of his love for mechanicalmodels, it is strange to report that he wasnot an engineer, nor was he useful withhis hands. Up to the age of 72 he wasunusually agile, but seemed to grow oldalmost overnight. He was an individ-ualist, a keen lover of travel, especiallyby boat. He never drove or owned amotor car and, as far as I can trace,never rode a bicycle.

Our Query ServiCeA REMINDER to readers that a

6d. postal order, crossed and madepayable to George Newnes Ltd., shouldbe enclosed together with the querycoupon from the current issue and thestamped, addressed envelope with everyquery submitted, for reasons which weregiven last month.

All enquiries regarding back issuesshould be addressed to the PublishingDepartment, and orders for books shouldbe sent to the Book Department andnot to the Editorial offices. --F. J. C.

102

WHEN arranging the Christmas party agreat amount of time and trouble isusually spent in compiling a list of

games and stunts to amuse the guests, butit is really surprising how seldom the pre-sentation of a play is included in the pro-gramme. It is all the more surprising inview of the fact that a great amount offun is derived from the actual preparationof the play, if carried out properly.

Mineral water cssesForm a rigid fnundatio

NEWNES PRACTICAL MECHANICS December, 1953

Tioq Po eid

Practical Information on the Erectionand Lighting Effects of a Stage for

Home Productionsr- -

in the middle of a dramatic speech than tofind the ground swaying under his feet. Thewhole stage should, on completion, be coveredwith carpet and the front boxed in.

An Ambitious StructureShould a more ambitious structure be

required a stage built up in the mannershown in Fig. 2 will be found quite useful.This, of course, entails a certain amount ofcarpentry work, but this is of such a simplecharacter that it is a job which may betackled even by an amateur. An advantage

Strong planks

Erecting the StageIt is possible, of course, to act the play

on the ordinary floor of the room, but wewill assume that we are really ambitious andare going to present quite a " professional "effort-and, therefore, the first thing is astage. An excellent dais, which will befound suitable for a not too ambitious pro-duction may be erected, as shown in Fig. t,from boxes and planks. Mineral water caseswill be found to make an excellent founda-

Screw eye

-a

Proscenium wire

Fig. t (Left).-Asimply -constructedstage made withplanks nailed to wooden

boxes.

Fig. 2 (Right).-Thistype of stage, built up ofcollapsible sections, iseasily stowed away

when not in use.

Screw eye

Stout battens screwed topicture rail and skirting board =.7--

I 1111111111111111E11111110 111111II

'' Side '

curtains

11=11171;1 i

Stage

The completed proscenium

Top curtains

tion, and builders' planks laid on top andnamed to the cases will hold the wholestructure together. It should be remembered,however, to have plenty of " foundation "to prevent the planks from sagging, for thereis nothing more disconcerting for an actor

Fig. 3 (Left).-Thissketch shows how theproscenium is erected,and indicates the posi-tions of the side battensand proscenium wire.

of this type of stage is that it is collapsibleand may be easily stored away for use withfuture productions. The portion illustratedrepresents one section, and the number ofthese which are to be employed is governedby the space available.

The ProsceniumAn excellent site for the stage is at an

opening between two communicating rooms,for here the proscenium is ready made andas these openings are often covered withcurtains, the problem of the curtain is auto-matically solved. We will assume, however,that we are not placed in so fortunate aposition and that we are staging the play inthe room in which the audience is to beseated. As we have gone to the trouble oferecting the stage we should do the jobproperly and cover in the front of our stageand erect a proscenium. A very simple andeffective method of doing this is shown inFig. 3. Here, as will be seen, two stoutbattens are fixed, one to each of the sidewalls, by screws into the picture rail and theskirting board. House-proud people may beafraid of the damage done by the screws,but these holes are easily filled with plasticwood and a touch of stain will complete

.4 four -sectionstage

Positions of hinges shown thus

the repair. Into the top of the battens screweyes are fixed and a wire is tightly stretchedbetween them. Light but opaque material is.hung in a strip at each side, and a narrowstrip suspended right across the room. Thuswe have our proscenium completed, and our" theatre " is now definitely taking shape.

About the CurtainOur next job is the curtain, and a very

convenient method of arranging this is shownin Fig. 4. This again is supported uponanother wire which is stretched in the sameway between the two battens. The distancebetween the curtain wire and the prosceniumwire should be about 6in. less than the depthof the top strip of the proscenium. An alter-native method of raising the curtain is shownin Fig. 5, but unless the room is very loftythis type of curtain should not be used,

December, 1953 NEWNES PRACTICAL MECHANICS 103

Proscenium wire

iScrew eye String anchored tocurtain

0

Screw eye

! Curtain

Anchor here

Fig. 4.-Details of the draw -type of curtain which is a very convenientarrangement for screening the stage.

as it will tend to cut down the heightthe opening.

The SceneryCurtains draped on the back wall form

the simplest way of overcoming the scenicproblems, and are very effective for certainplays.

Strips of curtain for side -wings completethe dressings for this type of setting, butfolding screens will do the job excellently.

For those who are prepared to go to alittle trouble very realistic scenery may bebuilt up and a glance at Fig. 6 will showthe construction of a typical screen. Thenumber of these which will be required willagain depend on the type of set desired andthe size of the stage. The best covering forthe screen is canvas, but stout paper willbe found very suitable if a temporary set isneeded. It is interesting to note that suit-able covering paper for this job is obtain-able already printed. It is possible forinstance, to obtain panelled oak windows,fireplaces, drawing -room decorations or out -

Hinged strutswhich may be usedif space permits

Fig. 6.-A useful scenery frame. The number ofthese required will depend on the type of set

used, and the size of the stage.

door scenes, all of which may be mountedand used in the manner explained above.This paper is also supplied mounted oncalico and this, of course, will stand muchmore handling.

of Lighting the StageA word or two about lighting may prove

useful, for it should be remembered thatthis may eithermake or, ruin theplay. One pointto make sure of isnot to have toomuch top lighting,as this will tend tothrow the face intoshadow. It ispossible, of course,to write a bookabout stage light-ing, but for ourpurpose the systemshown in Fig. 7will be found quitesatisfactory. A swill be seen, thefootlights a r emounted on apiece of wood andcardboard boxesact as reflectorsand shields. It isas well to have allthe stage lightingconnected to aseparate switch-board, whichshould be situatedbehind the stageand in the chargeof the " stage elec-trician." One pointarises here and that concerns fuses I It iswise to have spare fuse wire and an electrictorch handy just in case one blows in themiddle of the show.

Proscenium wire

Curtain 8. urtainScrew eye anchored here anchored

--- Aiii77iff-Mirratilr.:17:Cilnicfftrirragr.1,1m.

A.here

Screweye

...

,,..iiii."-"-NI

Puller

dl

Curtain A.

Double pulley

Curtain B.Weight

)String passes lithrough rings

. Weight --__As

1 rli1

III III

il

F g. 5.-An alternative method of raising the curtail , Fnown asthe tableau curtain. (Note the rings through which the hoisting

string passes.)

A Word on ProductionAlthough advice on production does not

strictly come within the scope of this article,perhaps a few pointers in this direction arejustified in view of the considerable amountof trouble taken to bill(' the theatre.

If you have never tried a play before, thebest type to start with is a short one -actaffair. Whether it is comedy, drama, ormystery of course depends on your individualtaste and the acting ability of your cast. Ifthe play is dramatic don't choose one withtoo many characters, as an over -crowdedstage will tend to destroy the effect andhamper the actors. Keep the furniturearrangement as simple as possible, andrehearse the play beforehand in the spacewhich you know will be at your disposal.Although it is just for fun, it is well worth

Position of

spending a little extra time in order to putover a really good show.

Several publishers issue books of short

lightingMINE 41111111111MUMIUMINUM 1111111111

Side battens

Stage

Cardboard boxlined withtinfoil

batten

Wooden flex cfuct4ss shown in A).end boxed in et back forms batten

/MPORTANT NOTE: Only new end heavily insulated flexshould be used.

Fig. 7.-An ideal lighting arrangement. It should be remembered thatinadequate lighting may ruin the play. Avoid having too much toplighting as this will tend to throw the faces of the actors into the shade.

1-a Theside

plays suitable for production by amateursat home, and such are usually of the one- andtwo -act type. The short " curtain raiser "is best for home production.

Moulding Leather DustASIMPLE moulding process developed

by the Plastics Research Co., Alhambra,California, transforms leather dust normallydisposed of as scrap into usable productspossessing many physical propertied oftanned leathers. Based on the dispersion ofadhesive powders with the leather dust, theprocess involves the use of a centrifugalmixer, and a compression press. It resultsin moulded leather -like sheets or parts.

The bonding ingredient consists of resinsin available powder form, such as thermo-plastic polymers, and B -stage thermosettingresins. Properties of the resulting productresemble those of the adhesive only withrespect to flexibility. The resinous com-ponents, may be pigmented prior to mixing,to obtain homogeneous colour effects.

104

MakinRubber ould

Wood Clamp

Fig. 2.-How the stamp rubber is prepared.

THE making of rubber stamps is aninteresting and profitable hobby; thisarticle shows how to do the work

with the simplest of tools and materials.Stamp -making may be roughly classed intothree divisions, i.e. (t) facsimile signaturestamps; (2) moulded rubber from printers'type; (3) made-up stamps needing novulcanisation.

Facsimile StampA small flat piece of metal plate will be

needed for these and it should be laid on atable perfectly level. Bend up a strip ofcardboard to form a long rectangle, aboutSin. by lin., lay it on the plate, pressing itdown with one finger, and pour in a littlebeeswax, sufficient to cover the plate about

/16in. (Fig.Let the wax just set, then remove the

cardboard rim. Before the wax can gethard, with a sharp pointed instrument writethe signature, penetrating the wax throughto the metal plate. When hard, clean outall tiny chips, then replace the cardboard

Fig. I. How the cardboard is bent and placedover the metal plate.

rim; all is now ready to make the plastermould. Sift some plaster of paris throughfine muslin, then dry the powder in anoven, making it hotter than the hand canbear. Grind it up to remove all lumps, thensift again. Mix the powder with water tothe consistency of thin cream, pour uponthe wax autograph and pat down lightly withthe end of a stick to force the cream into thelines of the autograph.

When the plaster is set quite hard itshould be a perfect facsimile of your signa-ture. Coat it with blacklead, taking carenot to fill in the eyes of your letters, placethe cardboard rim around it and make aplaster mould of it as before. This mould,from which the stamp will be made, shouldbe dried in the oven until all moisture isexpelled, otherwise it may crack during thevulcanising process.

For the stamps you will require some un-vulcanised rubber sheet about *in. thick;that used to repair motor tyres would do,but it must be unvulcanised, as the ordinarykind for applying with rubber solution isalready cured, and is no use for the purpose.

NEWNES PRACTICAL MECHANICS December, 1953

Rubber StampsA Practical Method of Making Facsimile and Ordinary

Rubber Stamps

Cut a piece as large as the mould, place themould (blackleaded as before) and rubberface to face, lay a piece of wood on eitherside and clamp together (see Fig. 2). Itmust now be heated gradually to 15o deg. C.to vulcanise the rubber. This can be donein a gas oven, but for the sake of economy

Fig. 3.-The wooden chase.

it is best to make up an improvised ovenfrom an old tin, placed over the gas jet.

During the heating process, give the screwof the clamp an occasional turn or two toforce the soft rubber into the mould. Abouttwenty to thirty minutes should finish the

Fig. 4.-The letters should be attached to therubber by means of rubber solution.

operation, after which the stamp can beremoved and trimmed ready for mounting.

Moulded Rubber StampsObtain a fount of printers' type suitable

for rubber stamps and make up the woodenchase shown at Fig. 3. The pieces A andB are nailed to the wooden base C, bothends being closed with pieces of wood. Thespace between A and B should just admit

Fig. 6.-The wooden mount for the stamp.

the size of the type chosen, and the insidesurfaces should be blackleaded to preventthe plaster sticking.

Set the name in type (reversed of course)and fill up the spaces at each end with theslips of metal provided with the fount oftype. See that the letters stand quite up -

Fig. 5.-Larger stamps, as shown, can be cutfrom sheet rubber and glued: to a wooden base.

right, and with a narrow strip of woodhammer them on top so that they lie level.With a small brush apply a little sweet oilto the type faces, then fill up the chase withplaster. This time there is no need to bakeit-sifting alone will do. The stamps aremoulded in rubber as for facsimile ones.

For small stamps obtain a child's rubberprinting outfit; the cheap ones with the typeonly about lin. high are most convenient.Plane up a piece of wood suitable for afoundation, and on the top stick with glueor cement a piece of sheet rubber; any oldmotor tyre's inner tube would be suitable.

Apply a coating of rubber solution to thesheet rubber and the bottom of the types,then leave until tacky. Next stick the letterson the sheet rubber (Fig. 4).

Larger stamps, as shown in Fig. 5, canbe cut from sheet rubber and glued to awooden base. A good plan is to attach asheet of paper each side.

Draw the desired figures or letters on asheet of stiff paper, lay a piece of carbonpaper underneath, coated side uppermost,then trace through. The paper can now beturned over and fixed with adhesive.

Details of an inking pad are given inFig. 7 and, for those who prefer to maketheir own ink, it is only necessary to dis-solve some aniline violet in hot glycerineand strain it while hot.

[This article is reprinted by request froman issue long since out of print.]

Fig. 7.-Method of constructing the inking pad.

December, 1953 NEWNES PRACTICAL, MECHANICS 105

X4.4

aintoConstructional Details of Simple Devices for Entertaining the Christmas Party

THE devices to be described can causequite a large amount of amusementand have the advantage that no diffi-

cult constructional work is called for. Mostof them can be made with materials whichare to hand and none of the dimensions orother details are in any way critical. Thework called for is also generally of so simpleand straightforward a nature that no oneshould experience difficulty with it, and thetime involved is very small. The games orpuzzles are so arranged that an electricalcircuit is completed, and this can cause anindicator lamp to light, sound a bell orbuzzer, or operate a radio loudspeaker, aswill be explained.

Operating current may be drawn from asmall dry battery, or a mains transformercan be used (with A.C. mains), if this ispreferred. The type of indicator which isused will depend upon personal preference,and what happens to be to hand. In somerespects an aural indicator (e.g., buzzer) ismost effective, though variety may beobtained by using different forms ofindicator.

Loop Threading PuzzleThis is shown in Fig. t and depends for

its successful accomplishment on a steady

Contact surfaces under map

By F. G. RAYER

" Buried Treasure "For this puzzle, a number of drawing pins

are pushed through stout card, and' a mapglued over to conceal them. The general

Stout wire

ScrewInsulated eyesleeving

Thin flex

'71

circuit

Fig. 1.-Threading the ring.

arrangement will be seen from Fig. .2, andif the map is glued to the top of a shallowcardboard box, this will conceal the locationof the pins.

The competitor is required to indicate onthe map, by piercing with the needle, the

Switch orPlug and sockets

0

Needle inholder

Flex

Fig. 2.-Treasure locating circuit.

hand and careful eye. A vertical piece ofwood is secured to a baseboard, and supportsa stout wire. This wire is bare, and some-thing such as 16 swg tinned -copper ismost satisfactory. Insulation is provided atone end only, as shown, and it is the taskof the competitor to pass the screw eye allalong the wire without touching it, untilthe eye and handle can be hung on theinsulated sleeve. This puzzle can havealmost any degree of difficulty, according tothe internal diameter of the screw eye andthe shape of the projecting wire. If eyeand wire touch at any point, the circuit iscompleted and the competitor has failed.

The competitor may also be required towithdraw the handle and eye to theiroriginal free position, without completingthe circuit by allowing contact between eyeand wire.

Tocircuit

a

Al/ drawingpins wiredin parallelin twocircuits

point at which treasure may lie. In theevent of the guess being correct, the indica-tor circuit is completed.

A means of changing from one pin toanother is desirable so that the puzzle isnot rendered useless when one spot has beenfound. This can be done by attaching aclip to the internal, pro-jecting goints of the Brew-ing pins, or by wiring upthe pins to a twitch orseries of scckets. Thelocation at which treasureis to be found can then bechanged at will accordingto which pin is broughtinto circuit.

Fig. 4.-Ring-tossingboard.

Common

Coin BoardThis arrangement is shown in Fig. 3, and

makes use of drawing pins pushed throughstout card or thin plywood. This boardshould be marked out with a checker pattern,and its dimensions are not important pro-vided a coin can bridge the gap betweenadjacent pins.

A length of thin tinned -copper wire isthen taken, and looped round the projectingpin points, about half the pins, selected atrandom, being connected together in thisway. If the wire is drawn tight and givena turn round each pin, no soldering shouldbe required. The free end of the wire formsone connecting lead.

A sheet of stout paper or thin card isthen pushed tightly in place so that the pinpoints project through it, and the remainingpins are connected, as before, to a secondlead. No contact between the wires of onecircuit and those of the other will bepossible, even when crossing, because of thecard. The completed board is best mountedin a shallow tray or box so that the leadscannot be seen.

Ir. use, the competitor tosses a coin uponthe board from sortie distance. If the coinbridges pins connected to each circuit, the

Fig. 3.-Coin-tossing board.

indicator will operate. If the pin does no.complete the circuit, however, it is " lost."

Ring -tossing BoardThe ring -tossing board shown in Fig. 4

is a somewhat similar arrangement, curtainor other metal rings completing the circuits

Upright rods Metal contact plates

2 a34 4

ARP

106 NEWNES PRACTICAL MECHANICS December, 1953

when thrown over the upright pegs. Thedifficulty of this game will depend upon thesize of the rings and the distance from whichthe competitor is required to throw.

The rods or pegs may be made from shortlengths of wooden dowel glued in holes ofsuitable diameter, and the metal contactplates may be cut from any thin metal, beingsecured over the ends of leads which passdown through small holes in the baseboard.

In this device, four separate circuits canbe completed, and these may go to an indi-cator board of the type shown in Fig. 5.The operating battery is wired in series withthe " Common " lead, and up to four indi-cator lamps may be made to light if fourrings are correctly. thrown. The numbersmay be painted on thin paper glued over thewindows on the inside, and various formsof scoring are possible, with the numbers notvisible until the appropriate lamp is lighted.

As with any other lamp indicator, thebulbs may be 2.5 or 3.5 volt torch -bulbs, andscrew -in holders are obtainable for these. Avariety of methods of employing such bulbs,either plain or coloured, will come to mindand a range of indicating devices can readilybe constructed.

Bell CircuitsThese are very straightforward, and are

shown in Fig. 6. Any small bell or buzzercan be used, and may be mounted, withbattery, at some convenient point under thepuzzle or game.

If mains operation is desired, then a belltransformer (or similar component with anoutput of about 4 to 6 volts) can be used,wiredas shown in Fig. 6. If a proper earth is

Windows with numbers

Fig. 5.-A simple indicator board.

available on the mains plug, then the coreof the transformer should be wired to thisto avoid danger of shocks if a breakdown ininsulation should arise. Frequently, onesecondary lead is similarly earthed for thesame reason. Such transformers cannot beused with D.C. mains. It is not recomlmended that mains voltages be used in anyof the puzzles, since these are far too highand the danger of shocks is very great.

Musical IndicatorThis type of indicator may be provided if

a radio receiver can be used, matters beingso arranged that when the circuit is com-pleted the loudspeaker operates. Thereceiver should be tuned to a musicalprogramme.

The existing loudspeaker may be used bycutting one lead to the speech -coil and takingwires from these points to the game. Theleads to the primary of the speaker trans-former should not be cut, as this wouldinterrupt the anode circuit of the outputvalve. In addition, unpleasantly high volt-ages will be found at this part of the circuit,particularly with mains receivers.

An external speaker may be connected asshown at " A " in Fig. 7, and this keepsdirect -current voltages out of the leads, so

that shocks are not likely to be felt. Thespeaker should have its own matching.trans-former with this circuit. If necessary, thereceiver speaker may be silenced by inter-rupting or disconnecting one lead to thespeech -coil.

Where low -impedance extension sockets

Bel/transformer

A.C.Mains

To game To game

Fig. 6.-Battery and mains bell circuits.

are provided, the circuit at " B " can be used,the speaker then requiring no transformer.A similar circuit can be provided by takingleads from the secondary of the outputtransformer in the receiver.

If the constructor has any doubt aboutconnecting up this type of indicator, it is

recommended that a buzzer or bulb be usedinstead. The loudspeaker type of indicatoris best used with a battery -operated receiverwhen no danger exists. If, however, it isused with a mains -operated receiver, propercare should be taken when wiring up toassure that there is no possibility of mains orhigh-tension voltages reaching the contactsurfaces of the puzzle or game. The .requiredisolation of the indicating speaker may be

To outputvalveanode

to 2/ifcondenser

To earth onreceiver

Fig. 7.-Circuits for musical indicator.

obtained by using a transformer, or con-denser of reliable type, as explained. Directwiring to the speaker should in no circum-stances be attempted, especially with A.C.j,D.C. receivers. An unsuitable form of con-nection may cause shocks or damage to thereceiver or speaker.

Togame

Toextensionsockets

Flashin

To game

Fairy LightsBy E. W. CROWE

THE usual flashing fairy lights leave ablack spot " between going off and

coming on again and, if any other source oflight is near, it detracts from the sparkle ofthe fairy lights when they are on.

The answer to this is to have anotherlight which will come on when the fairylights go off; this can be accomplished verysimply and effectively by a method which Ihave devised.

The type of flasherI used is one fromthe local chain store,which consists of asmall bakelite unitwhich plugs into alight socket and thefairy lights pluggedinto the flasher.

This circuit can bemodified as shown int h e accompanyingdiagram.

T h e continuouslines show the ortho-dox flasher circuit,and it can be seen thatby including the wiresshown dotted andusing a 55 watt, 23ovolt lamp that at first the fairy light bulbslight and as the heater causes the contactsto open the fairy lights go out and the55 watt lamp lights up to almost fullbrilliance. The result is very effective if thelamp is encased to appear as a star at thetop of a Christmas tree, or put inside thecoloured skirt of a fairy doll's dress. Natur-ally the bulb will have to be of the miniaturetype, similar to the type used in sewingmachines.

By turning the lampholder half a turn(by changing connection A and B round)both the fairy lights and the star will flashtogether, and by turning the bayonet pluground the star will light and the fairy lightsflash with longer periods off, since there is

Supply

Lamp holder

a small current flowing through the heaterconstantly.

I found from trial and error that the15 watt, 230 volt bulb gave the best result,whereas a lower resistance lamp tends tokeep the fairy lights on all the time.

Since all connections are made in thelampholder and bayonet plug there is nodanger, as there would be with temporaryconnections.

Flash era,

A Heating resistance

8/.metal Contactsstrip

L

15 Watt ,'30 voltminiature /amp

r

Plug

Ordinary lightingflex

Diagram of the modified flasher circuit.

PRACTICAL MECHANICS

To fairylights '

HANDBOOKBy F. J. CAMM

12/6, or by post 13/-. Itj Obtainable from booksellers, or i'

by post from George Newnes, :Ltd. (Book D e pt.), Tower

! House, Southampton Street,Strand, W.C.2.


An Flectric Liquid Mixer

Fig. 4.-The electric liquid mixer mounted onan adjustable stand.

ASMALL electric liquid mixer-not tobe confused with its larger brother thebatter beater-can easily be made

from the instructions given in this article.Using any low voltage or mains -type

motor, a mixer can be constructed which isstrong, compact and easy to handle. This canbe seen (Fig. t) by comparing one type ofelectric mixer with a standard hand drivenone.

A mixer consists of four parts, namely:(1) The electric drive motor,(2) The control unit,(3) Beater paddles and gears,(4) A stand (if required).

Fig. 3.-The cork is corkheld in position bydrawing pins or

elastic bands.

Shaft

The Electric MotorThis motor can be either:

(a) Universal mains ;(b) Low voltage AC or AC/DC ;(c) Low voltage DC.

The various types of motor, like theVarious types of control unit, have advantagesand disadvantages over each other, whichmight be physical (i.e. size), electrical,Mechanical or price. For example, with aUniversal mains motor its simplest controlunit need only be a rheostat, but a lowvoltage AC motor needs either a tappedtransformer or a transformer and rheostatas' a control unit. The final cost is about thesame, so the deciding factor in this case maybe speed control.

Constructional Details of a Useful but Inexpensive DomesticAppliance By J. D. MacDonald

The motors in the writer's scheme are invertical positions. No thrust bearing wasincorporated, as in such a small job this isnot necessary. However, if one wishes toavoid vertical motor running, then bevel gearscan be used with the motor in a horizontalposition.

Control UnitSpeed control on 24v. AC motors can be

obtained by either of the first two methodsand again is a matter of choice:

(s) A multi -tapped transformer ;(2) A rheostat in the secondary of a non -

tapped transformer. A rectifier must be incor-porated in each of the above cases if themotor is DC.

(3) A variable resistance in the motor fieldif the motor is DC. This is not always poss-ible as field leads are usually internally con-nected.

Driver

Paddle

( I :heel

)1,Pildgear

ler

wheel

Fig. 2.-The distance betweenthe paddle gear wheel centrescan be varied according to thebreadth of the beater paddles

employed.

Fig. t (Right).-A standard hand-_

driven mixer, andthe completedelectric mixerdescribed in thepresent article.

First groupto be

soldered

four. If an odd number of gars is u:ed,for example, three, then the beater paddieswill foul each other. The motor shown inFig. t has a 2 to t reduction gearing, thegear wheels being arranged as shown inFig. 2.

If the idler had been dispensed with thenthe beater paddles would have fouled eachother. This is obvious if the direction ofrotation is checked.

The paddles are made of silver steel, thedriving shaft being slightly thicker thanthe paddles and passing through the paddlegears. The paddles are hard soldered tothe shaft and are rectangular in shape asthey are easier to construct in this formthan any other.

It is rather difficult to hard solder fourpoints at right angles to each other, butwith a little ingenuity this can be done asfollows: obtain a cork of the same diameteras the inside diameter of the beater. Drivea hole down through the centre the thick-ness of the driving shaft. The hole can bemade by heating the shaft and pushing itthrough the cork. Place the four sectionsof the beater paddles round the cork atright -angles to each other (Fig. 3), and keepthem in place by means of drawing pins

(4) A mechanical gear box. This is rioteasy to construct and cuts out simplicity.Electrical control causes less strain on thehousewife, as can well be imagined.

Beater Paddles and GearsThe beaters can be either single or

double, and can be used with direct driveor reduction gearing. Reduction gearingenables a greater beating, power to beobtained. If the motor is vertical, then spurgears are required, but if horizontal, thenbevel gears. Gear wheels as used with con-struction kits are quite suitable. When usinggearing bear in mind that gear wheels mustbe in even numbers, that is 2 or 4, etc., butit is not recommended to have more than

or stout elastic bands. When one end ishard soldered push the cork along to thatend and solder the other. The cork hasthen to be cut away.

With double 1: eaters they are apt toseparate at speed due to centrifugal force.This can be overcome by soldering to theend of each shaft a bicycle spoke nipple withits square shank removed, and with a holedrilled through it to suit the shaft. Thenipples are then linked together with a pieceof looped silver steel wire as can be seenin the photographs.

The StandA stand is not a necessity ; the motor

can just have a 6in. dia. Perspex disc fitted


on the paddle side of the gears, as shownin Fig. I. In this case the mixer is placedon the.mixing jar and is then ready for use.Between the 'gears and the perspex a pieceof thin gauge brass sheet should be placedto prevent friction and wear.

A more permanent fixture is shown inFig 4. The mixer is held by two piecesof shaped brass sheet to a short tube, whichmoves up and down on a long tube fixedto a base. The mixer can be adjusted forheight by means of a fixing screw throughthe short tube. In Fig. 4 the sliding tubeis of copper, and the fixed tube of Sin.electrical conduit, with an electrical brassbush at one end to act as a stop and aceiling fixing plate at the other to enablethe tube to be fixed to the base. The powersupply flex to the motor passes downthrough the tube and base to the controlunit. The base is not fixed as it consistsof a hollow box and, therefore, when not in

Makin

Tomotor

Fig. 5.-These control circuits are suitable for low voltage D.C. For A.C. the rectifier isand the motor leads are connected direct to points a and b.

(a)7b

motor (b)

use the mixer can be put away in a cupboard.This makes a neat compact job.

Control CircuitsThe control circuits in Fig. 5 give the

basic diagrams for low voltage motors. For

removed

a mains motor a variable mains droppingresistance is sufficient. Signal lamps,switches and fuses can be placed in anysuitable position. For example, in Fig. 5a pilot lamp could be connected betweenpoints c and d.

a Perspecto raphA Device for Enabling Artists to Draw Buildings, etc., in Correct Proportion

THIS useful instrument will be founda great aid to the sketch artist. It isintended to he screwed to a tripod

stand, and this is the way to use it. Fig.is a view of the instrument minus the stand;you will see it consists of a horizontal barof wood with a vertical rod at one endand a sliding view -point at the other. Onthe rod are two crossbars, the top onecapable of movement up or down the rod,and itself fitted with two horizontal slides.

Now, suppose you desire to sketch a build-ing of some kind, say, for example, a church.

Fig. 3.-The patternfor the slides.

Fig. 2.-The view-point support.

Look through the eyehole, and arrange theheight of the tripod until the edge of thelower crossbar coincides with what will bethe baseline of your sketch. Slide down thetop crossbar until its front edge appears totouch the ground line of the church. Therod is marked in quarter inches, read off thedistance between the crossbars, and draw aline on your paper this distance above thebaseline already drawn. Raise the crossbarto a level equal to the roof of the church,then read off the distance as before and drawthe roof line on the paper.

Fig. 4.-Detailsof the tripod

legs.

4' 0"

Fig. I.-The fin-ished instrument.

.4

SECtiON OFEYE HOLE

Fig. 5.-The topof the tripod.

Moving the SlidesMovement of the horizontal slides will

now indicate the width of the church, andthe points on the roof where the steeplerises from. 'The crossbar can now indicatethe height of the steeple, and you will havethe body of the building drawn in correctproportions. Details are put in the sameway, such as windows, etc.

Hardwood is used for the work, tin. bylin. in section, the main dimensions beinggiven in Fig. t. The rod is a piece of lin.or fin. dowel rod, glued in a hole bored inthe lower crossbar with an inch projectingbelow; this is tightly fitted in a similar holebored in the perpendicular bar. To providea firm seating for this part of the rod, athickening block, fin. thick, is glued at theend of the bar.

Marking Out the RodThe rod is accurately marked into inches

by lines scratched half -way round, bin. linesbeing a quarter of the way round, and thein. lines being short cuts between.The top crossbar is similar to the bottom,

and should slide easily up and down therod. This can be effected by lining thehole with a piece of cloth or rubber.

The pattern for the slides at each side isshown at Fig. 3, which should be cut inthin sheet brass and bent to shape. The.edge of the crossbar, facing the artist, shouldbe marked in quarter inches, and numberedin inches from the centre outwards.

The View -point SupportThis has a small hole bored in, and is

screwed to a sheet brass slide, bent to theshape as in Fig. 2.

Bore a hole in the centre of the main barfor a tripod screw, and varnish.

For the tripod stand, cut three legs fromwood bin. thick, to the size in Fig. 4, andat each of the lower ends drive in a wirenail. Cut off the heads of these nails, andfile the shanks to a point, thus forming aspike to prevent the legs from slipping. Tothe tops fix a tin. brass hinge.

Now mark out and cut the tripod top asshown in Fig. 5, using wood sin. thick. Itshould then be varnished. The instrumentcan be taken to pieces and strapped to thetripod for easy carrying.


Making One stringed FiddlesConstructional Details of Two Instruments, Sometimes Known as Japanese Fiddles

THE two simple instruments hereindescribed are easily constructed, andboth have a pleasing, tone compared

with the cheap commercial fiddles of asimilar type.

The body of the instrument shown inFig. i is formed of cigar -box wood (approxi-mately tin. thick), but it is not just a cigar -box ; it is entirely reconstructed and reducedin length. The sides or " ribs are care-fully glued together with butt joints,strengthened by a triangular block of softpine about tin. wide, the full height of theribs glued and rubbed into each angle. Aneck- and tail -block, about *in. by 'in. insection, with the exposed angles rounded, isglued centrally on the inside of the top andbottom ribs respectively, also extending theirfull height. Glued to the inside of thebelly, so as to lie exactly under one foot ofthe bridge and running nearly, but not quite,parallel to the long axis of the body, is abass -bar, as in an orthodox violin ; andabout its own diameter tailwards of theother foot of the bridge a sound -post (seearticle Sound -post in Grove's " Diet. ofMusic ") is fitted tightly between the bellyand back, and perpendicular to them. Theabsence or improper fitting of these twomembers is the cause of much of the poortone emitted by both commercial andamateur -made one -stringed fiddles, and alsoof the undeservedly low opinion which manypeople have of these instruments generally.Both bass -bar and sound -post should be ofstraight -grained pine. The former shouldbe about sin, shorter than the belly, and theedge which is glued thereto *in. wide ; thedepth is graduated from fin. in the centreto about gin. at the ends, and the free edgeshould be well rounded from side to sideas well as curved from end to end. Thesound -post is a wooden rod of kin. dia.

The NeckThe neck is sawn out of a piece of *in.

mahogany (a keyhole saw was used for thecurved part of the " shoulder " and as muchof the straight part as is necessary). Theback of the neck is nicely rounded, and thefront, which forms the fingerboard, madetruly flat-any convexity in the length isparticularly to be avoided, as it may causejarring of the string in certain stoppings.The peg -box is formed like a small violinpeg -box (see dotted line on side elevationof head, Fig. a), being cut out with a chisel ;the cheeks are left Ain, wide at the frontand rather thicker towards the back. Thewidened part of the head is formed byglueing on two shaped slips of the samewood as the neck and finishing' them offflush at the front, back and top. The peg -hole may be bored before the peg -box iscut, at first no larger than the smaller endof the peg. The hole can be tapered witha large rat-tail file, carefully revolvedcounter -clockwise in the hole ; but properviolin peg -borers can be obtained. A home-made peg of rosewood or ebony, somethinglike that shown in the drawing, will lookmuch more in harmony with the rest of theinstrument than an ordinary violin peg. Ifyou have a lathe, the forming of the shaftis, of course, a simple matter, but whereonly one peg is concerned it will not be avery laborious process to shape it with afile from square to octagonal and from

octagonal to 16 -sided, and then to blend thefacets and finish off by turning the peg ina tube of glasspaper formed round it. Itis, of course, important to regulate the taperof the peg, and the hole, so that a goodbearing is obtained on both sides of thepeg -box. The " nut " which raises thestring r/r6in. off the fingerboard at thehead end is a slip of rosewood about sin.by AM. x Ain., fitted and glued into ashallow groove cut across the neck just belowthe peg -box, rounded on top and very slightlynicked in the centre for the string.

Tail -rest and Tail -pinThe tail -rest is another slip of rosewood

of about the same dimensions let into theedge of the belly for half its depth wherethe string passes over to the tail -pin: itshould be well rounded above, but needs nocentre nick ; its object is both to preventthe string cutting into the belly and to ease

M.

Fig. r. - (Right)Front, rear and sideelevations, showingconstructional detailsof a one-stringedfiddle.Dimensions may betaken by reference to

the scale.

Fig. 2.-(Above) Thebridge (A) is cut fromwell -seasoned oak andthe sound holes (B andC) are cut with a

fretsaw.

it will go right through the rib and block,but no farther. It should not be glued in,as the hole provides a view of the interiorof the body which may be useful at any timein locating defects or checking the upright-ness of the sound -post.

Bridge and StringThe bridge is cut with a fretsaw from a

slip of well -seasoned oak. In thickness thebridge is a compromise between an ordinaryviolin bridge and the shapeless chunksfavoured by the "Jap fiddle " manufac-turers, which gives it eventually an eleva-tion derived from the drawings of Japanesekoto bridges in " Music and Musical Instru-ments of Japan " (see Fig. 2A).

String -lengthThe string -length (from nut to bridge) is

shown on the drawings as 27in., the effec-tive string -length of a medium-sized

SCALE0

2"

FRONT ELEVATION

(TO REDUCED SCALE)

the angle through which the string has tobend at this point. The tail -pin, like thepeg, might be turned: but in our "M.r "(Monolin No. s) it was made by shapingthe end of a stick of rosewood tin. indiameter with file and penknife into the formof a miniature shouldered knob (see Fig, r)with a shaft about 4in. in diameter, to befitted tightly into a hole bored through thebottom rib of the fiddle and the tail -block.When the pin has been satisfactorily shaped,the shaft is cut off about lin. long so that

Peg hole

Nut

HEAD

FRONTSIDEELEVATION ELEVATIONOF HEAD OF HEAD

StringNeck

REAR ELEVA770N OFDOWBACK REMOVED)

Tail test

SIDE ELEVA770NOF LI.),DY

As the fingering of a one -stringed fiddle isnecessarily related to that of a 'cello wethink the latter might appropriately supplythe standard. The string with which theinstrument is mounted is that which seems tobe consistently adopted for the Jap fiddlesof commerce, namely a " banjo third steel,"tuned to Middle C. To the violinist or 'cellistthe use of wire strings on a bowed instru-ment may appear barbarous, but we haveproved that, with a properly designed bodyand bridge, the tone produced by their aid

110 NEWNES PRACTICAL MECHANICS

can be as pure and soft as anything thatcan be got out of catgut ; and theirsuperiority to gut in durability and indiffer-ence to moisture is obvious. The banjostrings have a loop ready made at one end,which can be slipped over the tail -pin ; avery small hole is bored in the peg toreceive the other end.

AssemblyWhen the ribs have been

it is best, before glueing onarrange the fitting of the neck.

SCALE0*

Nut

FRONT ELEVATION(TO REDUCED SCALE)

put together,the back, toThe face of

section roughly quarter -elliptical, about fin.by Qin. (see Fig. t). If the wood availableallows it, the shoulder of the neck may wellfinish flush with the body at the back, asin the " M,2 " instrument ; in " M.1" itdoes not extend so far, though the strengthen-ing blocks do ; the space between their endsis filled in with a kind of packing -piece.The extension of the fingerboard over thebody should be about Qin. thick, and reachto within sin, of the bridge, so that thestring may be stopped to s of its open length(3f in.), and thus give the instrument a com-

pass of three octaves.The back, a n d

then the belly, can

'Through Peg box

FRONT _ELEVATIONOF HE 0

Shoulder

REAR ELEVATION OFBODY (BACK REMOVED)

the shoulder which joins on the body mustbe quite square transversely, and shouldmake an angle of about 86 deg. with theplane of the fingerboard. Lay the ribson the bench, with the belly on top, thenprop up -the neck in contact with the bodyso that it stands as nearly as possible as itwill when fixed. Lay a straight -edge onth fingerboard, overhanging the body, andsee how high it stands off the belly at thelatter's centre (where the 'bridge will come);the distance should be just over fin. Adjustthe neck up or down until you get this right,then mark clearly on the neck where thetop edge of the rib comes. Take away thebelly, centre the neck to the axis of thebody very carefully, then holding or clamp-ing it in the correct position, make two smallbradawl holes, on the centre line, throughthe top block and rib into the neck (seedrawings), deep enough to take the two tin.or ain. round -headed screws which willsecure the body and neck together. Takingthese temporarily apart, enlarge the holes inthe body so that the screws can be pushedthrough them right up to the head, slightlygrease the screws, bring the parts together,and turn the screws home. It is desirableboth for strength and appearance to fit andglue into the angles between the neck andthe body (after the back and belly are on)blocks of the same wood as the neck,' in

SIDEELEVATIONOF HEAD

now be glued on, andcramped withweights; no nails orpins should be usedanywhere. Before thebelly is fixed it must,of course, have thesound -holes cut in itand the bass -barattached. The out-line of the formercan be enlarged fromthe illustration inFig. 2 (approx. halffull size) and cut outwith a fretsaw; orthe terminal eyesmay be bored with abit and the restcarved out with aknife. When theedges of the blockand belly (left inten-tionally a shadelarge) have b e e ntrimmed quite flushwith the ribs, thetail -rest and tail -pinfitted, and the bridgemade, the sound -postmay be inserted.Lower it through the

Fig. 3.-Front, rearand side elevations,giving constructionaldetails of a one -

SIDE ELEVATION stringed fiddle of alter -OF BODY native design.

December, 1953

sound -hole farthest from the bass -bar bymeans of a pin stuck in one end, and pareone or both ends until it will just standvertically inside the body, without anyforcing. It must now be slid into theposition described in an earlier paragraph,either by means of a piece of bent wire, ora string tied round it with two long ends,one issuing from each sound -hole.

VarnishingYou can now put a string on and get some

idea of the tone of the instrument. If itis fairly good, it will be better when thebody is varnished. Take the string off, giveall surfaces a final glass -papering and slightlyround all arrises, then apply to the body andhead only at least two coats of good quality" dark oak " varnish, with a rub downbetween. A preliminary sizing with a solu-tion of gamboge in methylated spiritis desirable. The neck is not varnished, butits surface is hardened by several applicationsof French polish each lightly rubbed downwith fine glasspaper or pumice -powder. Thevarnish on the belly should be scraped awayjust where the feet of the bridge stand.

The Second ModelWishing to make a second monolin for

ourselves, we debated the possibility of givingthe body the attractive convex outline ofthe. Japanese kokyu and samisen. Weremembered the various decorative uses towhich the constructor had formerly put thewood of a Canadian cheese -tub, and " M.2 "(see Fig. 3) was the result. The roughstringy birch needs a lot of preparing toget a fair exterior surface for varnishing,but the result pays for the labour. Themitreing is done by trial, and the jointsdepend mainly on the blocks-fitted andglued in while the ribs are secured withstring. The back and belly are of Bin.fretwood-the former " satin walnut " andthe latter " silver pine " ; the neck beingof dark walnut, the colour effect is verygood. The head has side additions for itsfull length, and the peg -box could thereforewell be cut right through the head in theOriental fashien with centre -bit and key-hole saw. The different form of sound -hole(Fig. 2) seems to be demanded by the curvesof the body. The tone is less brilliant thanthat of M.r, but is very pleasing.

A Socket SpannerDodge

A Handy Method of Threading Awkward StudsBy S. C. HUMPHREY

QUITE often, it is found, when thread-ing a, stud fitted in an awkwardplace that the " arms " of the die -

holder will foul surrounding objects, and if avertical die -holder and tommy bar are notavailable the job seems impossible withoutremoving the stud. By using a socketspanner to hold the die, as shown in thesketch, this problem can be overcome.

I have used this combination on cylinder -head studs, stub axle steering -arm bolts, andshackle pins where the thread had becomedamaged. In operation, a tight fitting splitcotter is inserted between the slot in thedie and one corner in the socket to preventit rotating. The ratchet spanner will befound useful where extension bar andtommy bar are not suitable.

Mr. Humphrey'smethod of using asocket spanner to holda die in awkward

places.


A Model Twin -cylinder Oscillating .EngineConstructional Details of the Single -acting Engine as Originally

Made for the Model Steam Launch "Vanesa

THOUGH the process was straight-forward, the construction of thecrankshaft was not easy. It will be

appreciated that there will be troubleif this item is a fraction out ofalignment. With a prefabricated shaft, thistrouble usually arises if the shaft holesare not absolutely parallel with each other,or if they are oversize, allowing too muchplay on the sections of shafting when placedin position. One way of overcoming this isto drill all webs together, tracing out thehole positions beforehand ; but four webstogether constitute a considerable thickness-rather too much for drilling by hand-sothe job was tackled as follows: An accuratesteel template was made. of the web size,holes included (Fig. 8). Then the fourbrass webs were cut and drilled very carefullyto this. Lengths of steel shafting were thenprepared and pressed through the web holes.Carefully aligning the webs into position,they were sweated with soft solder. Thenholes were drilled right through the webs andshafting, and pin rivets driven through.Finally, the sections of shafting marked Xwere cut away, the rivet ends filed flush, andthe whole cleaned up and given a goodpolish.

Centrepunch

Temp/ate

C/amp .3/8

'/8 Thick brass

Method of markingout webs

3/8'Webs 4 off

(Concluded from page 6o, November issue)

ments, but the final finish was applied byusing the drill brace clamped in the vice toserve as an impromptu lathe. The flywheelis made of brass, and is fluted to a depthof lin., leaving a boss tin. dia. throughwhich are drilled two 4 B.A. holes to take thesecuring grubscrews.

22 G. brass

Slots forpivor

course, to connect with the propeller coup-ling. But if the dog is required, the illus-tration, Fig. to, shows the actual dimensions.It is made completely of brass, with the pegsand bush sweated into the disc. The unit issecured to the mainshaft with a 5 B.A. grub -screw.

A stage of operations had now beenreached where it was possible to assemble

Securing boltcover

4f4x 20G. brass str p

Pivot hole

Slots cut for steampipes. Opposite sidefor exhaust -

Fig.

tor

Face blockscrew holes

iz.-Cylinder cover and supporting bracket.

Webs inserted into positonSections of shafting marked xcut and filed flush after soldering in

All ends riveted4 e over and Ned

Completed assembly

Fig. 8.-Details of the

FlywheelThe flywheel, of the dimensions given in

Fig. 9, was beyond handwork, so this I hadto have " turned " roughly to my require -

I/4"

Holesslightly

°Countersunk

06M.S. pins

Diagram showingposition of rivets

built-up crankshaft.

Universal DogThis, of course, need not be fitted, in

which case the pegs should be fitted to theflywheel instead. These are essential, of

5A5if

4 8.A4---- Grub screws

If+ 3/16

Fig. 9.-Perspective view' and section of the flywheel.

the engine, and test for alignment. At thesame time the overhanging support bracketwas fitted. This is a strip of brass, tin. widex 1/32in., shaped as in- Fig. cc. It issecured in position by the same screws thatalso support the mounting blocks (see Fig. s).This bracket assists in holding the mountingstandards firmly.

Fig.

Setting the Steam and Exhaust PortsThe illustration, Fig. 12, displays the

actual port positions in relation to the pivotand crank centres, with the correspondingmeasurements.

The operation was carried out as follows:Assembling one cylinder unit to the main

shaft crank, but without the pivot spring,the crank was rotated to a right-angle. Alittle " blue " was placed over the steamport on the cylinder face. The cylinderwas pressed home against the face block, andthen withdrawn, leaving a circular impres-sion, the centre of which was lightlymarked with the scriber. Rotating the crankto opposite right -angles, another impressionwas made and marked. The process wasthen repeated on the second cylinderassembly. The centres of these colouredimpressions are the exact positions for theports. Removing the blocks from the mount-ings, the centres were then " centre popped,"and a c/3zin. pilot drill run through to a

0

5/7;co.-Details of the driving dog.

4 B.A. screw

.-Fibre washer

CCFig. 12.-Diagram of steam and exhaust portlocations. (Note. In the other block the

position of the port is reversed.)

depth of 3/16in. The holes were thenopened out gradually to the required size asin Fig. 12. It will be noticed on the diagramthat the centre dotted circle is " edge on "to the steam port (right) and the exhaustport (left). This represents the position ofthe cylinder port with the crank at deadcentre (directly vertical). To obtain this, animpression was made at centre on the block,then both ports were gradually opened outuntil the inside edges nearly touched theedge of this impression. The result of thisis that when in motion, the ports begin toopen immediately the crank comes off centre,

which ensures thatsteam is acceptedfor nearly half thecycle, and the ex -

Bush haust begins to

Small hole clear without de-lay. This is very

Steam pipe important. Witha single - actingoscillating engine,

Barrel steam is accep-t ted on the down--0gdia brass ward motion only,

which is not quitehalf the completecycle (about 170deg.).7 herefore, itis important to getasmuch as possibleduring that time.If the holes wereleft in their firstdrilled state, the

cylinders would have to oscillate over a" dead"area of the block before meeting the ports,resulting in some loss of power. (That is whysome " toy shop " engines, although fast inmotion, do not always produce much power.)

Likewise, the exhaust should be got awayas quickly as possible, hence the exhaustport should be a shade larger than the steamport. It would be advantageous to havethis port " kidney " shaped. But it isimportant that care should be taken to keepthe " dead spot " at the precise measurement.If it becomes less than the width of thecylinder port, the block is rendered useless,as the steam merely passes through from thesteam port to the exhaust port. In theevent of such an error occurring, remove theblocks, fill all holes with brazing and re -drill.

0474-

44. -Fibre washer

Fig. i 4.-Lubricator details.


Exhaust port

7/16

ip

Standard

Crank at steam(full open)

341

5/32Dead spot withimpression ofCylinder portat vertical

team port

Pivot

Faceblock

214"

Stroke 3/4"Crank at exhaust

(full open)

Steam and Exhaust PipesThese have now been arranged as shown

in Fig. 6 of the March, 1953, issue (Vanesadetails). This arrangement is more satis-factory in the main, but if builders preferthe original style, the illustration, Fig. 13,shows the layout, which also includes thecondensation drum. This is not a condenserin the strict sense of the word, it merelytraps water, which would, until the enginehas warmed up, shoot up the funnel. Asimple form of superheating has obviatedthis trouble in the present arrangement. Theconstruction, however, remains the same.The pipes are 5/32in. for steam, and 3/16in.(copper) for exhaust. Having first beenannealed, they were bent to shape with theaid of wooden formers. They lead into theblocks via holes drilled at right -angles, theends first having a step filed on as shown.A good tight fit was ensured before solderingin. The " condenser " is merely a 2iin. xdin. length of brass tube fitted to the ends

11!- --wmirmr.t

Plumbers jointat X

Steam pipe from boiler

outlet

December, 1953

unions to the main steam pipe. Theextended handle is for convenience inhandling via the hatch cover of the engineroom skylight (see Fig. 9, March issue).

Displacement LubricatorThis is a length of 7/16in. dia. brass

tube bushed, and fitted both ends with4 B.A. screw plugs for draining and filling(Fig. 14). Two holes were drilled gin. fromthe top to enable it to be threaded on tothe main steam pipe, and soldered. Inci-dently, the new position is now centrallybetween the two cylinders (Fig. 6, Marchissue). One filling of oil is sufficient for onerunning of the engine, after which it has tobe drained and re -filled. Heavy cylinder oilis used. The function is basically asfollows : The part of the steam pipe thatis inside the cylinder has a small hole cr" nick " in it, and a portion of the steamenters through this into the lubricator, con-denses and sinks to the bottom, forcing upthe level of the oil, a little of which at a timefinds its way into the steam pipe, and iscarried with the steam into the cylinders.

Cylinder CoverThis is op-

tional, but ifrequired thegeneral arrange-ment can beseen in Fig. it.The function ofthis has alreadybeen explained;a step furtherwould be to en-close the wholeengine. I havenot yet donethis myself, butit would be anadvantage toconserve heat.The cover wouldof necessity haveto be of verylight material.So much for theengine details.The installationof the enginein conjunctionwith the boiler isshown in Figs.

8 9 of March, 1953, issue ofPRACTICAL MECHANICS. Finally, I wouldpoint out that if the builder chooses to fit thedriving " dog," the propeller shaft will have tobe a little shorter. Watch this point, therefore,when fitting. As an alternative, bring theengine slightly forward on the bed plate.

Lubricator

4// pipes stepped totit into blocks thensweated in

Fig. 13.-General arrangement of steam and exhaust pipes.

of the exhaust pipes. A 4 B.A. screw plugis fitted for draining -off purposes. Theexhaust outlet from the drum is a verticalin. dia. pipe. The extension from this to

the funnel was another length of lin. tubefitted with a well -fitting sleeve. The regu-lator is an ordinary stopcock fitted via cone

and the

.A CHRISTMAS GIFT PROBLEM SOLVED

rest.

At the present time, when many of the good things of life are either very expensiveor in short supply, the Christmas Season presents many problems-but when itcomes to buying gifts there is one simple and effective solution-you can arrange forus to send to your friends and relations who share your interests in the contents ofthis magazine, PRACTICAL MECHANICS every month from Christmas to theend of 1954.

Gift Subscriptions are not only original-they give pleasure and act as a reminderof your good wishes the whole year through.

An attractive Greetings Card will be sent at Christmas time in your namewith the first Gift Copy.

It is simple to arrange for we can send subscriptions to any address, at home orabroad, at the annual rate of 14/-.

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THE craters of the moon. How manyyears ago is it since man made hisfirst suggestion as to their origin?

Certainly no later than the birth of thefirst telescope. Two theories, diametricallyopposed to each other, have been propoundedwithout any clear lead being established byeither.

The first idea is that the craters wereformed by volcanic action. Whilst agree-ing that such action would at one time beintense on the moon-bringing into exis-tence mountain ranges such as theApennines (Fig. r) ; it is difficult to believethat the same agent was responsible for thegigantic walled plains, typified in formationby Ptolemy (Fig. t) with a diameter of115 miles. Others range between 5o andtoo miles in diameter. Even allowing for thelow gravitational force at the moon's surface-one sixth that of earth-the maximumdiameter of a Lunar crater or plain shouldbarely exceed 3o miles. Earth possesses fewcraters exceeding 5 or 6 miles in diameter.

e

V1

-,q

-----.3 - .

. . 0,ir

- , i,.. , , rt ft -14..

SectionthroughArzachel

)

P

SectionthroughPtolemy

Southpo/arregion

The Possible Causes of Their Formation

By WILLIAM ELLWOOD

Eruptive forces in the moon could hurldebris six times higher than would be thecase on earth, but that does not guaranteea crater six times as wide, let alone almost20 times as suggested by Ptolemy! Also,when considering these walled plains, thevolcanic cone or mountain in the centre isentirely absent. This does not help the vol-canic theory. Again, it is illogical tosuggest that the craterlets could be formed byvolcanic agency. Many of these small cir-cular craters are formed in the walls of theplains and ring craters. This infers thatthe debris after being hurled miles abovethe moon's surface, still possessed enoughheat energy to start an eruption of it's own,after it's return to the surface! Such acircumstance is extremely unlikely. It isa peculiarity, and in some instances a defectof human reasoning, to invoke the concept ofviolence when confronted with extraordinaryphysical or mental conditions. This ideaof violence-past violence in this case-ispresent when trying to interpret lunar. con-figurations.

Fig. i (Left).-The discof the moon is shown asseen through a tele-scope; that is, in the

inverted position.

Fig. 2 (Right).-An inces-sant meteorite attack onthe moon's polar regions.

APPr°achir91 "reo-it-e.,

\\I\ I

within the vicinity of our planet and it'ssatellite, it is sensible to suppose that agood number of them would be attractedto earth rather than the satellite, due to thelarger class of the former. A vast wandererof this description could pierce earth'satmosphere and crash, without appreciableloss in mass suffered by ignition of it'sexterior caused by air friction. As statedpreviously, no evidence is present of anysuch catastrophe.

As great areas of the moon's equatorialbelt are comparatively unmarked, whilst bothpolar regions are pitted with innumerablecraters, it seems that these terrific attackscame directly from southern and northernspace, relative to the moon. This infers anamazing if not impossible coincidence.

The meteorite idea suffers still furtherwhen we must admit that all the walledplains and ring craters are of nearly circu-lar formation. An attack mounted fromnorth or south would no doubt account forcircular craters at the poles, but the greaterthe angle of impact became towards the

Approaching meteorites

Polar /region

'-.Norrna/

Moon'scentre

Polarregion

Angle ofimpact

Sectionthrough aquadrant

of the moon

Massive and fast moving bodieswould seldom be influencedenough towards the moon'scentre, to el/ow their approachto coincide with the normal.

equator (Fig. 2), the meteorites would tendto plough furrows in the surface at thetime of impact, rather than form circulars \ / craters. The only alternative for

Equatorial regions the meteorite theorist, is to imaginecomparatively immuneMoon's- from attcentre_

\\,\s,

/1 \\°"'04/;)s, rneteOriteS

Fig. 3.-Anattack ema-nating fromnearly allsurroundingspace.

Bombardment by Meteorites !Volcanic action being unable to explain

all lunar phenomena, the mind takes a

leap into space-almost literally-and com-mences a shattering bombardment of thelunar surface by meteorites of all sizes, rang-ing from small fragments to colossal bodiesover 5o miles in diameter.

If such vast meteorites ever wandered

ack an incessant attack (over 3o thousandcraters have been mapped) from

nearly all surrounding space aimed un-varyingly at the moon's centre, andguaranteeing at the same time the im-munity of the already mentioned equa-torial regions known as maria or seas(Fig. 3). Even with this point suitablysettled, there remains the central mountainsof the ring craters to be accounted for.Arzachel with an interior mountain of5,000ft. is a good example (Fig. r).

The meteorite theory as a whole is fraughtwith difficulty, and as a result, generalopinion tends to favour the not -too -happyalternative of a volcanic causation.

There is, however, another explanationwhich may be more acceptable than either ofthe foregoing theories. It concerns therelationship of moon to earth and the result-

Earth

Orbital movement

410Fig. 5.-Diagram showing how one face of the moon

continued. The equatorial belt or, morecorrectly, that region of the lunar surfacelying almost at right -angles to the moon'sorbital plane, would suffer denudation lastof all.

This gradual drying up, spreading gener-ally from north and south, would neitherbe instantaneous nor complete. Innumerabledepressions in the swampy and semi -plasticsurface of the moon would still be full of

Moon and Hydrosphereinfluenced by Earth


ing action of the satellite's former hydro-sphere.

Covering of WaterIt can scarcely be doubted that the moon

at one time possessed a heavy covering ofwater. Present-day thought entertains thefact that volcanic action is a necessary func-tion in the creation of a hydrosphere. It is,therefore, natural that as a result of suchaction, no more severe than that experiencedon earth, the moon acquired a covering ofwater many thousands of feet in depth. Wemay mention here, that should the promin-ences of earth's crust or lithosphere besmoothed out to form a uniform surface,the whole globe would be covered by waterto a depth of some to,000ft. Applyingsimilar conditions to the moon, it becomesstrikingly obvious that the great mass ofearth would exert a tremendous influence onthe waters of the moon. This influencewould cause the water to pile up at two posi-tions on the lunar surface (Fig. 4). Theseas at a would be pulled towards earth.At the same time, the body of the moonwould be attracted somewhat less stronglyin the same direction, but sufficiently tocause the seas at b, at a position farthestfrom earth, to increase considerably in depth.This is identical to the action which givesearth its tides (plus the sun's influence ofcourse), only, in our case, the reciprocalattraction of earth to satellite is far lesspronounced.

Moon and Hydrospherefree from outside influences

.Hydrosphere

2 3 IFig. 4.-Foration of tidal bulges on the moon.

One -faced MoonIt is probable that long ago the tidal

waters of the moon would achieve fantasticdepths in the bulges. The effect of suchwater masses on the surface of the revolvingsatellite would be a slowing up or retardingof the moon's axial rotation, until finally,the time taken for one axial revolution wouldcorrespond with the orbital or periodic time(Fig. 5). The result of such action is toleave us with a " one -faced " moon whichhas persisted even after complete water dis-persion, though there can be little doubt thatthis condition was achieved ages beforewater vanished from the moon's surface.This appears to be confirmed by the vastgrey plains of the equatorial belt where theremaining waters would accumulate and liealmost stationary, relative to the moon'ssurface, until final dispersion into space.This last condition would be inevitable, dueto the small mass of the satellite. Thereremains, nevertheless, the intriguing questionwhether any water remains on the oppositeor unknown side of the moon. After the" one -faced " condition was obtained, earth'sgravitation would no longer assist in dis-persing water on the opposite hemisphere !

The moon's polar regions would be thefirst to suffer water denudation as dispersion

To

Earth

2The hydrosphere is exaggerated to aid clarity.

water. Time after time the main watermasses would be dragged back and forthacross these areas according to the moon'sposition in its orbit. The plane of thisorbit makes an angle of 5 deg. 9 min. withthe ecliptic or orbit of earth round the sun.

Tidal ActionIf we take one of these depressions

(Fig. 6) we find that, so long as the timefor the moon's axial rotation is less thanthe periodic time, the imprisoned watermust pursue a clockwise movement (anti-clockwise for the southern hemisphere). Allirregularities on the circumference of thisdepression or lake would be smoothed outby tidal action due to earth's gravitationalforce. The material of these ;rregularitiesand further material scoured from the nowfairly circular bowl or " crater " would bedeposited evenly round the- circumference bytidal action. Infrequent but widespreadinundations of the whole area by the stillactive main water mass would add furtherdebris and silt to the outer walls, eventuallygiving them a remarkable but not impossibleheight-the average being 4,000ft. abovethe surrounding surface. As the floodreceded, water would in many cases betrapped in cavities in the walls, thereby

December, 1953

The only sound explanationfor the Moon's orbital andaxial period being identical,,lies in the assumption thatthe satellite once possesseda heavy covering of water.Due to libration we are ableto view nearly three fifthsof the lunar surface.This, however, does notmaterially affect our present

discussion.

Axialmovement

is constantly presented towards earth.

commencing the formation of the craterletspreviously mentioned.

Inside the main " crater " or walled plainthe slowly circulating water would, centuryafter century, continue to erode the innerwalls. As the water level gradually droppedmuch of the eroded material would bedeposited on that area of the crater floorwhere least movement of circulating waterwould occur, that is, in the centre. Noneof the central cones or mountains rise to thesame height as the surrounding walls. Inthe case of a very large walled plain, thehuge volume of water involved wouldpossess the characteristics of a land -locked

'Water

Sections showing -tidal effect

Clockwisemovementof water

Lunar

NorthPole

Intermediateshape

Water

x

75

Earth

A typicaldepression

Finalshape

Fig. 6.-Birth of a lunar crater.

sea, and no mountain would be formed. Theeroded material in this instance would bedeposited fairly evenly over the entire floor.It is important to remember that the floorsof the walled plains and ring craters areinvariably much lower than the surfaceoutside the walls. This strongly suggeststhat the original site was a depression inthe moon's surface!

Viewing the evidence as a whole, it wouldseem to support the latter theory more con-vincingly than that of a volcanic or meteoritecausation. It uses the moon's former hydro-sphere as the tool and earth's gravity asthe wielder of that tool. Final water dis-person would leave vast grey plains, suchas Mare Tranquillitatis (Fig. r), as an ever-lasting testimony of the long extinct but -once mighty hydrosphere of the moon.


STEREOSCOPIC p r u Re s

Fig. 4.-Simple wooden frame which enablesstereoscopic pictures to be taken with an

ordinary camera.

THE industry and activity with whichthe major American film companieshave recently gone in for three-

dimensional films has raised hopes that, atlast, the cinema may be able to capturesome of the life and feeling of the theatre.

The development of three-dimensionalmoving pictures represents the latest phasein an art, which, surprisingly enough, wasthe subject of experiment by Friese-Greeneway back in the 189os, and long before thatthe Victorians were enjoying stereoscopicstill pictures.The Eye and Stereoscopic Vision

When we look upon a distant scene, thelight which enters each eye is formed bythe lens of the eye into an image on theback of the eyeball (Fig. r). This regionof the eyeball, which is known as the retina,is composed of a myriad of tiny nerveendings, and the light falling on each onesets up impulses within it which are trans-mitted to the brain.

That the brain is receiving two images canreadily be proved, either by quickly closingand opening each eye alternately in rapidsuccession whilst looking at a near object,whereupon the object will appear to jumpsideways at each changeover of the eyes, orby displacing one eyeball by gently pressingwith the finger, when two distinct images willbe seen.

The fact that each eye is receiving aslightly different image, whilst with botheyes open we only see one, indicates that thebrain is blending the two images into one.

But, now look at a distant scene and closeone eye, and with most people the viewimmediately loses depth. Some people findthat closing one eye destroys the illusion ofdepth more than when the other is closed,and an unfortunate few are barely able tosee in depth at all.

When a photograph is taken with acamera we are virtually recording the sceneas it would be viewed through one eye. Thecamera lens replaces the lens of the eye andthe photographic plate replaces the sensitiveregion at the back of the eyeball. Theresulting picture, whilst being artisticallyattractive, lacks perspective or depth.

Stereoscopic Still PicturesSuppose, however, that there are two

cameras, one replacing each eye, assembledso that the lenses are the same distance

A Brief Description of the Systems Used for Obtaining ThemBy " PHYSICIST "

apart as the pupils of the eyes, which fora normal person is about 21in. (Fig. a).Two photographs of the same scene can betaken simultaneously, or, if there is no move-ment, at different times. Provided thephotographs are arranged so that the onetaken with the left-hand camera is viewedexclusively by the left eye and the otherexclusively by the right eye, a three-dimen-sional effect will be obtained.

This technique was well known to theVictorians and the viewing apparatus theyused was called the stereoscope. It usuallyconsisted of a wooden frame in which thetwo photographs could be mounted side byside, each one some distance behind amagnifying lens (Fig. 3). The viewer lookedwith one eye through each lens and thedistance between the photographs and thelenses was adjusted until the illusion ofdepth was produced.

With stationary objects there is no needto have two cameras, and stereoscopic pairsof photographs can be taken even with aninexpensive box camera. The camera ismounted on a wooden frame (Fig. 4), fittedwith side pieces spaced a distance such thatwith the camera pushed close up to one sidepiece, the distance between the other camerawall and the other side piece is aiin.

Retina Eyeball

Object -4 -

Optic nerve to Lens ofthe brain the eye

Fig. I.-The eye. Diagram showing how lightfrom an object enters the eye via the lens andforms an image on the retina at the back of the

eyeball.

Separate exposures made with the camerapushed up against each side of the framein turn will give prints which produce athree-dimensional effect when viewed in astereoscope.

Effective as the stereoscope may havebeen, its usefulness is limited by the factthat only one viewer could look in at atime and there was only one position fromwhich to view. Consequently, it could neverbe applied in the cinema, where the screenis viewed by 'an audience seated over a widerange of position.

Anaglyph Method for Still and MovingPicturesAnother system for obtaining the illusion

Fig. 2.-Principle ofthe twin lens stereo-scopic camera. Notethe marked similarityto the eye in respectof image formation.

of depth, known as the anaglyph method,was used in the 192os and dispensed withthe viewing frame. The photographs weretransferred to printing blocks and printed oneon top of the other, but slightly offsetlaterally with respect to each other. Onephotograph was printed in red and the otherin green -blue ink.

The stereoscopic effect was produced byviewing the composite print throughspectacles, in which one of the eyeglassesconsisted of a piece of red glass or celluloidand the other of green -blue glass. The green -blue light from one print was preventedfrom entering one eye because it could notpass through the red eye glass, whilst thered light was similiarly prevented fromentering the other eye. Each eye, therefore,saw only one image and a three-dimensionaleffect was produced.

This system was successfully adapted tomoving pictures in the middle 193os, whena film called " Audioscopics " was made andin which a series of startling effects wereproduced.

Unfortunately, there were several practicaldisadvantages to this system. Apart fromthe communal use of viewing spectacles, thefact that one eye was constantly receiving ared image and the other a green -blue imagewas liable to cause eyestrain and fatigue; nor

Observer1-2%.

JPhotographs

Fig. 3.-Diagram showing the position of thelenses and photographs in a stereoscope.

was it possible to make coloured pictures bythis method. Therefore, in spite of thecomparative simplicity in making and show-ing films by this method it has not beenfurther exploited.

Polaroid Method for Stereoscopic Picturesin Natural ColourThe way to make and project colour films

in depth has long been known, but the prac-tical application had to wait until thediscovery of a new material, known as" Polaroid," enabled suitable viewing glassesto be made cheaply.

Light is propagated as a series of vibra-tions and in a beam of light these vibrationsoccur in all directions perpendicular to thedirection of the beam. It is possible, by

Photographic plate or filmCamera lens

Camera ;ens

Photographic plate or film

Cbject


passing the beam of light through an appara-tus known as a Nicol prism, to confine thevibrations to one direction only, and such abeam is said to be " plane polarised." Ofcourse, one does not notice any differencein the beam of light, but if a further Nicolprism is placed in the path of the emergingbeam and rotated, a setting is found whereno light gets through the second prism.

The discovery a decade or so ago of thematerial known as " Polaroid" which provedto be a substitute for the Nicol prism, andcould be produced in large sheets, meant thatstereoscopic colour films became a possi-bility.

In this system, the picture is recorded,via a twin lens camera, on two synchronisedfilms. The projection of these films is morecomplicated than hitherto. With the exist-ing projection equipment, two projectors haveto be run synchronously, with one of thetwo films in each and adjusted so that theright amount of separation of the images onthe screen is achieved. A suitable" Polaroid " filter is placed in the path ofeach projector beam, so that the light in eachbeam is plane polarised and the filters areadjusted so that the plane of polarisation inone beam is at right angles to that in theother.

The screen is viewed through spectacleshaving glasses made from " Polaroid " andthese are adjusted so that the image from theleft-hand projector is viewed by the left eyeonly and vice versa, and the stereoscopiceffect is thus produced.

The advantages to the audience in thissystem are obvious. Natural coloured pic-tures can be shown and eyestrain due tomono -colour fatigue is relieved, but scrupu-lous care must be taken during projection toensure that the correct separation of the

image is obtained on the screen, or othertypes of eyestrain and headaches are apt tooccur.

The present projection difficulties, whichrequire each cinema to have four projectors,synchronised in pairs, if there are notto be breaks in the projection of the film,will no doubt be overcome by the use oftwin track projectors with split beams oflight.

Lenticular screen

(a)

Correspondingstrips fromeach film

(b)

Fig. 5.-(a) Showing a section of a lenticularscreen.

(b) Enlarged diagram of a cross-section ofone lens of the screen.

Lenticular Screen TechniqueNevertheless, there are aesthetic and other

considerations which have encouraged thedevelopment of other systems for producingstereoscopic effects. It has been rightlyargued that the ideal system would be onein which the audience were freed of theobligation to wear spectacles, or other viewing

aids, and such a system has been evolved inwhich the image separation is done auto-matically at the screen, and is reputed to bein use in two Moscow cinemas.

Basically, the screen can be imagined asbeing made up of a large number of longnarrow, vertical, cylindrical lenses andimmediately behind each lens, correspondingstrips of each film are projected side by side(Fig. 5), so that the left eye sees only oneimage strip behind each lens and the righteye sees only the other. A complete imageis thus seen by each eye and a three-dimen-sional effect is produced.

Presumably, in this system, back projectionis employed and suitably spaced grids in eachprojector beam break up the two picturesinto strips of the right dimensions.

There is no record of this system havingbeen used anywhere other than in Russia andit is difficult to see how a large audience dis-persed throughout the cinema can look at thescreen and each receive a truly stereoscopicpicture.

Wide Screen and Stereophonic SoundA recent American invention which uses

a wide curved screen is being used in cinemasthere and is said to give an illusion of depthwhich is enhanced by the use of multiplesound tracks and loudspeakers distributedthroughout the auditorium.

The pictures are taken and projected onconventional cameras and projectors, and theillusion of depth is produced because, owingto the size and shape of the screen, the eyeis not able to focus on all of it at once.

This system has recently been demonstratedat a London cinema, and it is reported thatmore are being fitted with the special equip-ment.

Items of Interest

Interior of the Solar Dome in the Royal Observatory at HurstmonceuxCastle, showing the Newbegin telescope with Greenwich 4 -inch photo-

graphic heliograph for photographing the sun.

Powerful New PlaneEngines

IT is reported thatRolls-Royce, Ltd.,

has developed twonew versions of thefamous Avon engines,which power some ofthe world's fastestair c r aft, includingNeville Duke's recotd-breaking HawkerHunter, the Comet IIand the Canberra.Details of the per-formance of the newR.A. 2t and the22 are still secret.

The Comet II,which has Avon axialflow turbo -jets of6,5oolb. thrust each,gives a cruising speedaround 500 m.p.h.

The new enginesare designed todevelop considerablymore thrust. T h eR.A. 21 has produced8,o5olb. thrust testrating and the R.A. 227,1501b. thrust testrating.

Measuring the MetreTHE international standard meter is kept

in a vault beside the observatory ofMeudon, close to Paris. Several countrieshave one of the set of keys for opening thedoor that leads to this vault, and it cannotbe opened unless the representatives of allthe countries employing the metric systemare present at the same time.

An inaccuracy crept in when the firstmetre was made. It was intended the metreshould measure one ten -thousandth part ofthe quarter of the earth's meridian passingthrough Paris ; and it is two -tenths of amillimetre short.

But it will no longer be necessary to keepthe standard metre with such care. At arecent congress, wavelengths were studiedwhich could be used to give the measure ofa metre with the greatest possible accuracy.The spectroscope revealed that the vibratoryphenomenon of spectral lines was of extra-ordinary regularity, and it is on that basisthe calculation of the metre will be made.The red cadmium band has a wavelengthof 0.64384696, and a metre would be equalto this length multiplied by 1,553,164.12. It'sall very simple. Thus the metre can bereproduced anywhere in the world and beabsolutely accurate.

Oil Consumption in BritainLAST year Britain used about twice as

much oil as before the war, andexported over 12 times more than in 1938.

In 1938 the import of refined oil was82 per cent. of the total. To -day it is21 per cent. In 1938, also, two-thirds ofU.K. petroleum imports were from theWestern hemisphere. Now they come fromthe Middle East, while the West suppliesonly one -fifth.


WITH few tools, average skill, and apiece of 3/16in. Perspex, tolin. x4-1in., it is possible to make quite a

professional -looking deflector for the bonnetof your car. This useful accessory assistsin keeping the windscreen clean by divertingthe stream of air caused by the forwardmovement of the car to points beyond thearea of the windscreen, and carries with itmud and flies which would otherwise settleon the screen.

The angle to which the deflector is shapedlargely depends upon the distance of itsfixing point from the windscreen, the longerdistances having a more acute bend. Witha fixing point of 3ft. 8in. the following typehas proved successful, but it will be readilyseen how the actual shape can be adapted tosuit different conditions.

Marking Out and CuttingThe shape is first set out on the backing

paper on the sheet of Perspex (Fig. s) andwaste removed with a coping saw. Theedges should be cleaned and polished beforeremoving the backing paper.

A former should be made upon which thesoftened Perspex may be shaped. This canbe of wood or clay as shown in Fig. 2. A

The deflector, bent to shape, andfitting in place.

Alternatively, blocks of softwood can beshaped and fixed to the baseboard. Thismakes a good job, but, perhaps, may be toopermanent for merely one shaping.

A Useful Accessory Which Keeps the Windscreen

Clean by Deflecting Flies, Mud, etc.By C. T. MACKLIN

softened in boiling water or, preferably, ina gas or electric oven set at a low tempera-ture. For those with no experience in hand-ling this material, first soften one of thewaste corners from the original sheet so asto get some idea of the length of timerequired to achieve plasticity. PlasticisedPerspex is pliable at too deg. to Ito deg.centigrade, and excessive heat will causesmall blisters. It is quite easy to open theoven door to test for softness, and this shouldbe done after two minutes.Bending the Perspex

When in a pliable state transfer thePerspex quickly to the mould and applypressure at the points shown, first in thecentre with a clean rod or the rounded edgeof a thin piece of wood. Another pair ofhands should assist by applying downwardswith two pads of smooth cloth at pointsA and B (Fig. 3).The Mounting Clip

It should be possible to get some sort ofstandard clip to fix the deflector to thebonnet or the bonnet motif. Alternatively,suitable clips, as shown in Fig. 4, could bemade from strip brass. The deflector shouldbe fixed so that it leans backwards slightly,as shown in the illustration at the top ofthis page.

If the instructions are followed closely, theresult should be as effective as the commer-

cial deflectors now onthe market, both frontthe points of view ofutility and smart appear-ance.

Are ioV2°

Fig. 1.-How to mark out the shape.

spadeful of clay from which stones have Softening and Bendingbeen removed is excellent as it can easilybe rolled to a slab I4in, thick, after whichthe waste clay in the centre is removed witha hacksaw blade. The same tool is after-wards used to make a smooth surface. Theclay should be allowed to harden beforeshaping the Perspex.

A Perspex 4'

Approx 0; thick

Shaped block Baseboard's

Fig. 3.-Method of bending the Perspex.

ready for

Wood orclay shape

Fig. 2.-The former,mounted on a baseboard.

Having prepared the mould withsurfaces the piece of flat Perspex

smoothis then "Plastics Art and Craft"

READERS interested in working withPerspex, Catalin, Casein Plastics, and

cellulose acetate, and the special purposeplastics such as Nylon, Crinothene, etc., andespecially those who wish to make articlesfor the home or accessories such as thatdescribed on this page should obtain a copyof Plastics Art and Craft, published byC. Arthur Pearson Ltd., at 8s. 6d.

This well illustrated and comprehensivebook explains how to make a number ofarticles such as trinket boxes, cigarette box2s,table lighters, bangles, serviette rings, studboxes, powder bowls, hair brushes, etc.

Fig. 4.-Brass clips for fixing the deflector in The use of the necessary tools is alsofully described.place.


Buotescent lightingWith Notes on the Construction of Fluorescent Lighting Fittings

IT is now over twelve years since the firstcommercial fluorescent lamp appeared onthe market, and during the last few

ears of the war this type of light sourceprovided better lighting for vital production,as well as saving electric power for otheruses. To keep tube production at a peak,only one type of lamp was made-a 5ft.tube which consumed 8o watts and gave asmuch light as a t50 -watt bulb. The 5ft.tube is still the most popular size, althoughits light output and operating life have beengreatly increased since those early days, butnew a complete range of lengths has been

Base cement Electrode

Base \Exhaustpin pip

for Domestic and Workshop Use

Ballast EquipmentIf such a discharge tube were to be con-

nected direct to the power supply, more andmore of the gas -filling would ionise, allowingthe current to build up to enormous propor-tions, until the electrodes were completelydestroyed. In practice, however, the currentis controlled by a " ballast " which is wiredin series with the tube to keep it operatingwithin its rated limits. The ballast may be awire -wound resistor of high wattage rating,and in some fittings a filament lamp isused, this producing light also, improvingthe overall efficiency of the circuit. Theseresistance and lamp ballasts are not recom-mended as usually more power is lost in theballast than is taken by the tube itself, thustaking away the advantage of high efficiency.

Choke ballasts are the most suitable, andare almost universally used, as theoreticallythere is no loss of power in a pure induct-ance. In the practical case, even the best

Inside surface of tube coatedwith fluorescent powder

Space inside tube filled with Argon gasand Mercury vapour

Nroduced, from the ain. 15 -watt to the8ft. 125 -watt.

Before proceeding to a description ofsimple fluorescent lighting fittings for thehome constructor, details of the constructionand operation of fluorescent tubes and theirassociated equipment are given. This willhelp the constructor to understand thebehaviour of the equipment and provide valu-able data for the repair and maintenance ofexisting commercial fittings.

The Fluorescent TubeIn contrast to the ordinary filament lamp

the light from which is only a by-productof heating the metal filament, the productionof light from a fluorescent tube is achievedin two stages. A current passing throughthe filling -gas first produces ultra -violetradiation which strikes the powder coated onthe inside walls of the tube. The powderthen absorbs the radiation and converts it tovisible light, the colour of which may bevaried by varying the chemical compositionof the powder. The fluorescent tube does thisjob of " production and conversion " veryefficiently and, in fact, its efficiency expressedin light -units per watt is three to four timesthat of filament lamps of comparable wat-tage.

Fig. t shows a cut -away view of a modernfluorescent tube showing the electrodes whichact as anode and cathode each alternate half -cycle, the powder coating, the exhaust pipand the end caps. The internal filling is ofEgon gas at a low pressure, and mercuryvapour which contributes to the productionof ultra -violet energy.

Fig. a (Left).-A cut-away view of a modernfluorescent tube showing

the electrodes.

Fig. 3 (Right).-A" glow" starter switchand details of its canister

and socket.

ballast dissipates a few watts, but these areof a negligible order. Thus all the powertaken from the mains is passed to the tubefor conversion into light, and the circuit is ahigh efficiency one.

In effect, there is an inductance and a re-sistance across the mains, and this results in

PP correction Ballastcondenser

Fig. 2.-Starter circuit.

a power factor of less than unity. As thevoltage across the tube is roughly half themains voltage, the power factor (PF) is gener-ally of the order of 0.5. Although this factdoes not show on the domestic electric meter(kWh), the authorities recommend the cor-rection of the power factor to reduce the" wattless current " in the mains. Correctionis effected by wiring a suitable condenseracross the supply at a point near the tubecircuit, and units are marketed, containingboth choke and condenser known as highpower factor (HPF) ballasts.

By W. McMILLAN

by switching on the power, as the mainsvoltage is not sufficiently high to start ionisa-tion of the gas. To overcome this the cir-cuit in Fig. 2 was devised and operates asfollows: Mains are switched on, starterswitch closes, completing a series path withthe tube electrodes which heat up to operat-ing temperature in a few seconds- Thestarter then opens and, interrupting an in-ductive circuit, produces a high -voltage" kick " which is sufficient to ionise the gasand start the discharge.

Canister contains glow -starterand radio suppressorRadio interference

condensersuppressor condenser

Glow starter

81 -metal

The most common type of starter switch isthe " glow -switch " (Fig. 3), which consistsof a piece of bi-metal sealed in a gas -filledglass bulb. On switching on, the mains volt-age appears across the starter and ionises thegas -filling producing heat which bends thebi-metal. The bending metal short-circuitsthe starter completing the circuit to the tubeelectrodes. Being short-circuited, the gasis extinguished and cools, bringing the bi-metal back to its original shape, again open-ing the starter, providing the kick to startthe tube conducting. The action is notrepeated since the voltage now across thestarter is the " tube voltage " which is toolow to re -ionise the gas.

Instant StartingIt has been found that most tubes will

start successfully without the inductive

Starter SwitchBecause of the length of the path between Fig.

the electrodes, the tube will not light merely

Ballast

AC. Mains

Instant -starttransformer

Starting-strip on tube

4.-Circuit for instant starting, using atransformer for heating the electrodes.


kick, provided that the electrodes are broughtup to operating temperature, and any staticcharges on the surface of the tube areneutralised. The circuit in Fig. 4 showsa method of heating the electrodes, using atransformer. This circuit enables the tubeto start within less than half a second ofswitching on, and has been classed as theinstant start circuit. For reliable operationthe tube should be near an earthed fittingor have a thin metal strip fixed along itslength, the strip being earthed. Specialgraded " instant start " tubes are now madewith this strip already fitted. The earthedstrip provides a leakage path for the minutestatic charges which form a barrier tostarting.

FittingsIn the simplest case, a fitting can be made

by mounting the ballast, starter and tubeholders on a stout wood batten about zlin.by ain. cross section, the length being cutto the nominal length of the tube used. Sucha fitting is shown in Fig. 5 with (a) a simpleballast circuit, and (b) a HPF ballastunit which incorporates the starter. Thewood batten should be given a coat of size,an undercoat and a hard white enamel top

Starter Ballast on tray whichfits into batten

Edge turned back tostiffen reflector

Reflector

coat so that it may be easily cleaned andact as a good reflector. Where the ballastis considered too clumsy or heavy forceiling mounting it may be concealed in theloft or cupboard, although the leads shouldnot be unreasonably long. This leaves onlythe tube and starter mounted upon the woodbatten.

A commercial type batten fitting is shownin Fig. 6. When complete, this is a self-contained unit ready to connect to the mains.Construction may be of zo swg aluminiumor mild steel, with the end pieces riveted orwelded to form a rigid structure. Rigidityis of prime importance, since any tendencyto bend might allow the tube to slip fromthe holders. The metal should have anenamel finish for best reflecting properties.

To all of these fittings a reflector can beadded if required, of aluminium or steel, thegeneral shape of which is shown. Slotsshould be cut in the top of the reflector toallow about to per cent. upward light toprevent what is known as " tunnel effect."

Woodbatten

Tubeholders

Starter (a)

( b)Fig. 5.-Simple fittings made by mounting theballast, starter and tube on a wood batten.

Ballast

A.C. Mains

110 vol starters

Fig. 7.-Circuits for series

Series OperationWhere 1:mited space is available, or where

a short fitting is required, two of the shorttubes may be wired in series and mountedside by side. Circuits for such a combinationare given in Fig. 7. The first has twoseparate "glow switch " starters of the Ito -volt type, and the second uses a " double -glow " starter (Atlas patent), which has a4 -pin base. For two ain. tubes in series,a 3o -watt ballast is used, while for two 24in.

Fig. 6 (Left).-Detailsof a commercial type

batten fitting.

Fig. 8 (Right).-Twotypes of simple fittingsusing series pairs of

tubes.

A.C. Mains

Ballast

I 'Double -glow' starter

operation of fluorescent tubes.

of these variations between different brands,it is wise to buy the ballast first and buildaround it. The sizes of other componentsare standardised, making replacement easier.Good ballasts should last indefinitely, theusual cause of failure being the breakdown ofthe PF condenser. Starters should outlastseveral tubes and their life will be preservedif, when the tube reaches the end of its life,it is not kept switched on, trying to light.The end of tube life is marked by heavy

To replace ceiling rose

A more ambitious unit with'Egg -crate' louvre to reduce brightnesswithout reduction in total light output

zo-watt tubes a 4o -watt ballast is required,and two 24in. 4o -watt tubes require an 8o -watt ballast. The importance of using aballast of the correct voltage rating cannotbe overstressed, as any departure from therated running conditions shown in the tableresults in short tube life and poor perfor-mance.

Two sketches are given (Fig. 8) of simplefittings using series pairs of tubes, the dimen-sions of which vary according to the size oftube chosen and the size of the ballast. Thecross section of the ballast will govern thedimensions of any fitting to incorporate it,although a smaller and lighter fitting isobtained by remote mounting of the ballast,in which case its size is not critical. Nearlyall ballasts other than the 8o -watt type are ofsmall section-usually about 21in. bywith the 8o -watt about 31in. by zin. Because

Ballast may be mountedbetween tubes or externally

Side panels of'Perspex' or'Crinothene

black rings at its ends, a yellow glow and aninability to light soon after switching on. Ifkept switched on, the starter will keep try-ing to start the lamp, damage itself, and over-heat the ballast also.

Installation Hints,Where the fitting is constantly in the field

of vision, eye -fatigue through glare is likelyto be experienced to a slight extent. A metalreflector as already described should be fittedto conceal the tube from that direction, oran egg -crate louvre may be applied as inFig. 8. Equally, the apparent brightness ofthe tube surface may be reduced by a diffus-ing cover of Perspex or Crinothene, and thistreatment is recommended for all domesticinstallations where the tube is seen.

Indirect lighting " is the ideal form, where(Continued on page 533)

Nominal lengthin inches

18242436486o

16in. diametercircle tube

Table of Tube Sizes and Operating DataTube Volts Average light

Rated current across output throughWatts (amps.) tube life (lumens)

15 o . 3 56 42020 0.35 62 62040 0.88 5o 1,1603o 0.34 103 1,20040 0.41 108 1,70o8o 0.85 1o6 3,00040 data not available 1,36o

Averageoperating

life (hours)5,0005,0005,0005,0005,00o5,0005,000

The figures for light output apply to Daylight and Warm White colours only. Natural,Peach and Mellow tubes are slightly lower, but have better colour properties.

The 18in. and 24in. lamps may be operated singly on either 1 to volt or zoo/25o volt mains,or two in series on zoo/25o volt mains with suitable ballast. No ballast is made for single tubeoperation of the 24in. 4o -watt tube, which should therefore be used only in pairs.


New Short Research AircraftBrief Particulars of the Sherpa Swept -back Wing Monoplane

ANEW aircraft, which may revolutionisethe shape and performance of futureaeroplanes, has made its first flight

in Belfast. It is the Short Sherpa, aresearch aeroplane, designed as a fore-runner of high-speed aircraft flying at veryhigh altitudes.

411

make the aircraft more manoeuvrable at highaltitudes.

The Sherpa itself is a research aircraftand is not capable of high speed, but thelessons learned from its tests will form thebasis of design of future high-speed civil andmilitary aircraft.

[43- 355.1. 13.-1-4?31'- ;If

GROUND UNE

The Sherpa, designed and built by ShortBros. & Harland Ltd., of Belfast, has tworevolutionary features. It is the first air-craft ever to fly with an " aero-isoclinic "wing-a new technique patented by Short's-and instead of conventional ailerons andelevators, it has inclinable wing tips whichact as controls.

The aero-isoclinic wing has been designedby David Keith -Lucas, Shorts' chief designer.Instead of being stiff it is relatively flexible,and the inclinable wing tips serve as bothailerons and elevators. These tips compriseabout one -fifth of the total wing area andmake it possible to dispense with the normaltailplane and elevators.

Turbomeca EnginesThe Short Sherpa is a swept -back

shoulder wing monoplane, with two smallTurbomeca jet engines mounted side by sidein the centre of the upper part of thefuselage, just behind the cockpit.

This aircraft is the third new aircraft to

9.-1-124

V

Side and front elevations giving the leadingdimensions.

The Short Sherpa aircraft fitted with the new " aero-isoclinic" wing.

When a normal swept -back wing bendsupwards due to air loads it automaticallyloses incidence and lift at the tips. Thisgives rise to a form of instability which canbest be illustrated by an aircraft pullingout from a dive. The additional load whichcomes on the wing due to the pull outcauses the tips to bend upwards, and onlosing lift at the tips, which are well towardsthe rear of the aircraft, it pulls out stillmore sharply.

This is overcome on the Short isoclinicwing by making it twist as it bends. Forthis reason the wing has to be more flexiblethan usual and special types of aileronshave to be used.

Additional ManceuvratilityIt is expected that the inclinable wing -tip

controls will be markedly superior to flap -type controls at transonic speeds and will

313.- e

Plan view showing theinclinable wing tips and

swept -back angle.

be produced by Short Bros. & Harland inthe past 12 months, and is the second wing -research aircraft to come from their designteam. The Short S.B.5-the adjustablewing 'plane, which is investigating swept -back wing problems-has been flying forsome months.

The Sherpa was flown on its first flightby Tom Brooke -Smith, chief test pilot toShort Brothers.

Plastic Wheels for LawnmowersSELF-LUBRICATING plastic wheels-for

use on a 331b. lawnmower-which arestronger than aluminium or cast ironhave been produced from styrene copolymermaterials at half the cost of wheels madefrom other materials and metal. Thewheels, designed by the Newark Stove Co.,Newark, New Jersey, are moulded of Kra-lastic, and when finished and fitted withrubber tyres weigh only 18oz.

The wheels are injection -moulded in twohalves, with the axle housing moulded aspart of one half in a sleeve -like projection.The wheel halves are removed from themould, de -gated, and riveted together. Thetyres are slipped around the wheel rims. Thesteel axle shaft (dipped in light oil during

assembly) is inserted into the sleeve and fast-ened in place by nuts and washers. The oilseals the sleeve, preventing abrasive particlesfrom entering, and eliminates wear and scor-ing of the bearing surface. The oiled axlerides directly in the housing and gives self-lubricating properties to the mower.

The finished wheel survived a shock testwithout evident damage, in which under aweight of 7olb. it was rolled over kin. lugsfastened to a hard surface at a speed of27 r.p.m. for 6o hours. To determine theexpected service life the mowers were putthrough a field test of 200 hours, approximat-ing two to three years of normal service.This test showed a minimum of wear and nosqueaking.


The Properties of Glass, and the Simple Tools and Processes Used for Working It

THERE are two main methods which canbe employed for joining tubes of un-equal diameter. The first method is

to draw out the larger diameter tube as shownin Fig. 23a. It is then cut off at the point

O

JointFig. 23.-a and b. First method of joining

tubes of unequal diameter.

which corresponds to the diameter of thesmaller tube and the joint is worked inexactly the same manner as for tubes of

OFig. 24.-a, b, c and d. Second method of

joining tubes of unequal diameter.

equal diameter. Fig. 23b shows the appear-ance of the finished joint.

The second method is more complicated,but repays the extra work which is put intoit.

Fig. 25.-Making " T" and " Y " joints.

The end of the larger diameter tube isfirst closed and rounded. Whilst still hot,it is heated at the end by means of a smallpointed flame (Fig. 24a). When a red spotappears at the end of the tube, it is blown

By E. HARRIS MORGAN, B.Sc.

(Concluded from page 67, November issue)

out into a small bulb (Fig. 24b). This smallbulb is heated in a slightly larger flame andblown out with a single strong puff. The thinglass is cleared away from the edges of thehole which now appears as in Fig. 24c. Thesmaller diameter tube (already flanged) isheated up together with the large diametertube and, when quite soft, they are pressedtogether and pulled slightly apart as before.The working of the joint follows the normalprocedure as described previously. Thefinished joint appears as in Fig. 24d.

" T " and " Y " JointsThe procedure to be followed for making

" T " and " Y " joints is similar to thesecond method for joining tubes of unequaldiameter. In this case, however, a hole isblown in the side of the tube as shown inFigs. 25a and 25b. Two of the open endsare blocked with bungs and a rubber blow -tube connected to the third free end. The

14"app

(c)

INCHESOF WATER

- 10 -- a -- 6 ----- 4 -- 2 --- 0 --2 -- 4 -- 6 -- a- /0 -

'4\Sm.m. GlassTubing

Mercury orcoloured water

Fill to scale b"

(6)

joint is made and finished in the normal way.Figs. 25c and 25d show the appearance ofthe finished joints.

Sealing Wires Into GlassIn order that a seal with good mechanical

properties may be obtained, a metal which

O0

.giass rod

Glass bea90

Fig. 26.-Sealing platinum wire electrodesinto glass tubes.

has the same coefficient of expansion as glassmust be used. Other properties of the metal(such as its capacity of being " wetted " by

SCALE FOR USEWITH WATERIN MANOMETER

/2

/0

8

64 -2O

2

4

6

8

10

/2

Interval. I"

SCALE FOR USEWITH MERCURYIN MANOMETER

-72GO

Interval 9/210{

(Reduce lengthof manometerfrom /4"to 7")

INCHES OF WATER

(b)

56

24

/2

- 24JV

48

60

72

INCHES OF WATER

4

2

2

4

The greater the angle the moresensitive the manometer

11111MOMMIIIII

111111111111.11111111111114441.1111111117WAIMIII=Vertical interval

i for waferMercury calibratibn as (b)

Fig. 27-a. The manometer with scale calibration for water.c. A sensitive manometer.

b. Scale calibration for mercury.

122

glass) must also be taken into account. Ingeneral, however, the only really suitablemetal for soft glass is platinum. Platinumis a very expensive metal, but fortunately wecan make the seals by using very short lengthsof platinum wire.

The first part of the process is to blow ahole in the glass at the required point.This is accomplished by heating the glasswith a fine pointed flame while maintainingan air pressure inside the apparatus. In thisway the glass is blown as soon as it softens,and a very small hole is produced.

A short length of platinum wire is nowtaken and one end bent as in Fig. 26a. Thewire is held in a pair of pliers, and, whilebeing heated is touched with a fine spindleof glass as in Fig. 26b. When cool the wireis placed in position as in Fig. 26c and thework heated and manipulated to form a goodseal. Fig. 26d gives a view of the completedseal.

Making Simple ApparatusThe reader who has mastered the tech-

niques described in this article will be ableto carry out the construction of many usefulsimple pieces of apparatus, some of whichwill not at first appear to be so very simple,but careful planning of the order of workwill reduce most operations to the applica-tion of known methods. At first, of course,there will be many failures, but this is trueof any craft, and only patience, practice,

PLAN VIEW

.Showing position of electrodes

SIDE VIEW

1.t=111116)Tube drawn and mercury introduced

3"

Tube sealedFig. 29.-Details of a mercury tilt switch.

and a thorough understanding of underlyingprinciples can enable the high degree ofskill of the competent glassworker to beattained. Most of the failures which occurin glassworking are due to either lack ofthoroughness in annealing, or to the toorapid heating of the glass. Glassworkingprocesses cannot be hurried; in fact, " TheSlower the Better " might be a good mottoto hang over the work bench.

A few simple pieces of apparatus are des-cribed below for the purpose of practice inthe craft.

The ManometerFig. 27a gives details of a manometer suit-

able for measuring the gas pressure at thesupply point or the air pressure developedby the blower unit. The gas pressure isabout seven inches of water, and in this casethe manometer is filled with water. Theoptimum air pressure for a blowlamp isabout forty-eight inches of water. Thismeans that if the manometer is filled withwater it will be unduly long, but it may bemade of convenient length if it is filled withmercury, and in this case the dimensionsgiven in the diagram may be used. It

NEWNES PRACTICAL MECHANICS

3"_____.

PLAN

PERSPECTIVEVIEW

Fig. 28.-Details of Hero's steam engine.

should be noted that if the manometer isfilled with water, each scale inch shouldactually be one-half inch. In the case of amercury -filled manometer the calibrationwill, of course, be different. Fig. 27b givesdetails of the calibration of a mercury mano-meter. In Fig. 27c is shown a more sensitivemanometer which measures lower pressures.The method of calibration is indicated inthe figure. A small spirit level should befitted to the base board of the manometer,and the instrument should be calibrated andused with the base board horizontal.

SIDE VIEW

Hero's Reaction Steam Turbine (circa ADroo)The piece of apparatus described below is

a modification in glass of a very early steamengine working on the jet reaction principle.Full details of the instrument are given inFig. 28. It is included as an exercise insome of the simpler processes. To operatethe instrument, the bulb is half filled with

' water by alternately heating and cooling thebulb with the jet under water. The lowershort length of glass tubing is held in a pairof pliers and the bulb heated over a smallflame. When the water boils, the reactionof the steam issuing at the jet causes theengine to spin rapidly. By taking care notto overheat the bulb, the engine can berefilled and used repeatedly. Do not attemptto refill immediately after using; allow thebulb to cool first.

Mercury Tilt SwitchThis switch is of simple construction, but

provides an exercise in closing a tube, seal-ing in wires, and drawing -off and sealing.Figs. 29a, b, c and d give the sequence ofoperations in the construction of the switch,with appropriate measurements. (The latterare not important, and can be varied to suitindividual requirements.)

ThermostatThe thermostat is an instrument used for

maintaining a constant temperature in, forinstance, a bath of liquid. The model des-cribed here has a fair degree of accuracyand can be varied to control over a wide

December, 1953

range of temperature. Fig. 3oa gives theessential measurements and the associatedcircuit. A relay taking as low a current aspossible should be used to prevent excessivedrain on the battery. The sequence ofoperations is as follows : The wide boretube is sealed to the narrow bore tube; theend of the wide bore tube is closed androunded, the narrow bore tube is bent intoa U -bend; the platinum electrode is sealedin position. The sliding electrode should bean easy fit in the narrow bore tube, and isheld in position by a rubber band. Thebulb of the thermostat is filled with tolueneand the narrow tube with mercury. Thetemperature at which the instrument operatesis varied by altering the position of thesliding tube for fine adjustment, or by alter-ing the amount of mercury in the narrowbore tube for coarse adjustment.

ConclusionThe articles described above are merely

given as exercises in glassworking, and it isappreciated that the reader might not wishto construct all, or even any of them, for

1

0Water level ifthermostatis used to

controltemperature

of bath

J!* fa.

Sm.m.die.

Toluene

Copper wire

Rubber band

alm

Platinumwire

-NR

Heater

Platinum wireelectrode

Contacl-s normallyclosed

Relay coil

o

Mercury Thermostat' contacts

Fig. 30.-a. A simple thermostat. b. Thewiring diagram of the associated circuit.

actual usage. The processes involved docover, however, the essential techniques, andit is a simple matter to extend these tech-niques to the construction of many otherpieces of apparatus; for instance, a modelgasworks, or the hot water system of a house.

Whatever job is tackled, the reader isadvised to plan the work thoroughly. Adiagram of the apparatus (preferably full-size)should be drawn and the order of operationsworked out so that no awkward situationsarise during construction. Above all, workto the diagram, so that the finished articleis the neat and exact piece of work that isthe hallmark of a good craftsman.

J

FORBy F. J.

SCREW THREAD TABLES, 5/-, BY POST, 5/3.

REFRESHER COURSE IN MATHEMATICS, 8/6, BYPOST, 9/-.

GEARS AND GEAR CUTTING, 6/-, BY POST 6/6.

DICTIONARY OF METALS AND ALLOYS, 10/6, BYPOST I I /..WIRE AND WIRE GAUGES (VEST POCKET BOOK),

3/6, BY POST 3/9.

ENGINEERS.------,CAMMNEWNES METRIC AND DECIMAL TABLES, 3/6, BY

POST 3/9.

PRACTICAL MECHANICS HANDBOOK, 12/6, BYPOST 13/-.

SLIDE RULE MANUAL, 5/-, BY POST 5/6.

MATHEMATICAL TABLES AND FORMULAE, 5/-,

BY POST 5/3.

From GEORGE NEWNES, LTD., TOWER HOUSE, SOUTHAMPTON STREET, STRAND, W.C.2.


You'll be glad you chose one of the

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The Prince Charles Sets are very popular amongstGauge ' 0 ' enthusiasts because of their accuracy and true-to-liferealism. Sturdily built they offer you best value for money.

Clockwork Set.-Locomotive, Tender and 2 Bogie Coachesin B.R. blue or green, with oval metal track, 48in. x 78in. Track ismade up of twelve 131in. curved rails and six 104in. straight.

Price 110.2.6

Electric Set.-Locomotive, Tender and two Coachesas cloFkwork set with scale Permanent Way track, 72in. x 126in.Track made up of twelve 18in. curved rails, five 18in. straight andone 18in. terminal rail. A set with all the advantages of positivespeed and direction control, operating from A.C. house mains.

Price 121.15.0

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The c Enterprise is specially recommended to modelengineers with the skill, the time and the simple tools to build thispowerful live steam locomotive from a set of parts. All componentsare finished, ready for assembly. The complete set of finishedconstruction parts, including illustrated booklet on how to buildthe model. Price 18.15.0

For those who prefer, the ' Enterprise ' can be supplied alreadyassembled. Price 110.0.8

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Here's the most comprehensive andfully illustrated Gauge '0' Catalogueyet published.Make sure of your copy-write now,quoting Ref.: C0/12. Still only 1/6.

For those more mechanically minded write for theModel Shipping and Engineering Catalogue. Thisis indeed a manual of model engineering that everyamateur engineer will want to possess. Writequoting ref.: MS/12. Price 2/-.

We invite you to visit our showrooms either in London, Manchester or North-ampton to see our display of working models including complete layoutsin Gauge '0' and '00'. In addition there Is everything to meet the needsof the Model Builder.

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Standard 6 CoupledTank Loco.You should have atleast one of these 0.6.0 tt.maid of all work' on

your layout. It is a power-ful model fitted with first classor electric.

Clockwork ...Electric Spur Drive, 12 volt

mechanism, either clockwork

Price £7.14.0Price £8.17.4

Scenic Backgrounds for Gauge '0' and Gauge '00' modelrailways beautifully printed in full colours. Four interchangeablepictorial sheets, each different in type but all matchingso that they may be set up in any order. Size of each sheet2ft. llin. x 9in., making approximately 12ft. of realistic scenery.Price the set of 4 sheets, 12/6. Including Purchase Tax. Postage6d. extra.

New Goods Brake Van.It is fitted with long wheelbase, correct type axle boxes,anti -friction metal wheels andstandard couplings. Cast ironwheels can be fitted at anadditional cost of Is. 10d.

Price 14/ -

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Single and doublearm, complete withladders and red andgreen spectacles.Bracket Signals asillustrated, 16/4.Also availablesingle arm Signal,7/10. Two armSignal, 10/6.

LT D Head Office and Works

NORTHAMPTONLONDON 112 HIGH HOLBORN W.C.I. MANCHESTER 28 CORPORATION ST.


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December, 1953

HIGHSTONE UTILITIESSolderingIrons. Ournew stream-lined iron isfitted with

a Pencil Bit. 200'250 v. 50 watts, 11/6.cost 6d. Standard Iron with adjustablebit, 200/250 v., 60 watts, 13'6, post 6d. HeavyDuty Iron, 150 watts. 1618. post 8d. All partsreplaceable and fully guaranteed. SmallSoldering Irons, for use on gas. 1/4. post4d. Resin -cored solder for easy solderinged. packets or large reels 5/-, post 9d.New Headphones, 101- a pair. Balancedarmature type (very sensitive). 12/6 a pair.Both post, V-. New Single Earpieces,316. Bal. armature type, 4/8 ex-R.A.F.earpiece. 2(6, post 4d. Headphones, ingood order. 8/- (better quality. 7/6). allpost 1/-. Headphones with moving coilmike, 151-. Similar phones with throatmikes. 12/8. post V-. Headphone Cords,1/3 a pair, post 3d. Replacement Bands,1/3, post 4d. Wire Bands, 6d.(All Headphones listed are suitable foruse with our Crystal Sets.)

Bell Transformers.These guaranteedtransformers workfrom any A.C.Mains, giving 3, 5,or ft volts output at1 amp., operate bulb.Miner or bell. Will

supply light In bedroom or larder, etc.PRICE 9/-, post 8d. BELLS for use withelthe the above or batteries. 6/6. post Od." Big Ben " Chimes. Housed in CreamPlastic Case. Easily connected to giveTwo -Note Chime from Front Door, andSingle Note from Rear: Operated from 6-9volt Batteries or Transformer (shownabove). 23/-, post V-.Ex-R.A.P. 2 -valve (2 -volt) MicrophoneAmplifiers as used in plane inter -corn..in self-contained metal case ; can be usedto make up a deaf -aid outfit, intercommuni-cation system, or with crystal set; completewith valves and fitting instructions, 20/-.post 2/-. Useful wooden box with partitionsto bold amplifier, 2/- extra. Ditto, lessvalves. 10/-. One -valve amplifier, completewith valve, 10/6, post 1/8.Hand Microphones, with switch in handleand lead, 4/6. Tannoy, 6/-. Similar instru-ment. moving coil, 7/6. All post 1/-. Masktype with switch. 3/8, Post 4d.Sparking Plug Neon Testers with vest-pocket clip. 3/3, and with gauge, 3/8. post 3d.S.B.C. Neon Indicator Lamps, for use onmains showing " live " side of switches,etc.. 3/6, post 4d. Neon Indicator, completewith condenser (pencil type), with vest -tertc..

cke7/8t clip. indispensable for electricians,

, postCrystal Sets.Our latest Modelis a real radioreceiver, whichis fitted with apermanent crys-tal detector.Whynot have a set inyour own room ?121, post 8d. DeLuxe Receiverin polished oakcabinet, 18/6,post 1/-.

Spare Permanent Detectors, 2/- each.When ordered separately, 2/6. With clipsand screws, 2/10, Post 3d. Headphonesbrand new, S. G. Brown, G.E.C., etc., 15/-,23/-, and super -sensitive, 301-a pair, post 1/-.Microphones. -Just the thing for im-promptu concerts, room -to -room communi-cation, etc. Bakelite table model, 8/9.Suspension type. 8/6. Post 6d. MikeButtons (cajbon) 2/ -. Moving Coll, 4/8 ;Transformers, 5/-. All post 4d. each.Rotary Transformers, 24 v. input; Output1,230 v., .2 amp. in case with suppressors,etc.. easily converted to run as a high -voltage motor. 251-, carr. 5/-. Also 12 v.input; Output 6 V. .5 amp. ; 156 v., 10 mA. ;and 300 v.. 20/240 mA.. 22/8, carriage 6/-.Morse Keys. -Standard size keys wired towork Buzzer or Lamp. 31-, post Bd. Slightlysmaller keys, 2/6, post 4d. BUZZERS.319, or heavy duty. 416, Post 5d.Terminals, brass. 2BA. mounted on strip6d. pair. .0005 Airspaced Variable Con-densers, 2/6, post 4d-00003 twin gang withtrimmers. 2/8, post 4d. 24 volt. 15 m/m..M.E.S. Bulbs for model railways. etc..1/- each. 10/- doz., post 4d. Wander Plugs,Brass, 1/6 doz.. post 4d. Fuses. -1 amp..1 lin., packet of 10. 2/6, Post 3d. Also 150 mA.and 250 mA., same price. Hydrometers,Standard Type, 6/ -, post 6d. Ex-G.P.O.Telephone Twin Bells, with box. 5/-, post 1!-.Single Telephone Bell. 3/6, post 6d.Bargain Parcels, of really useful equip-ment, containing Switches, Meters, Con-densers, Resistances. Phones, etc.. 10/ -or double assortment, 17/6 : treble 25/-.All carriage 2/-. This country only.Meters. 15 v.. 21in. rn/c., 9/6 : 150 v.. 2in.m/c.. 10/- ; 3.5 amp.. 2In., T C., ; 4 amp..21in-, T.C., in case with switch, 9/8 ; 100 mA-21n.. rn/c., 716 : Meter Units containing1-500 microamp. movements. 7/-, post 11-.

All meters post extra.

Money refunded if not completely satisfied.

HIGHSTONE UTILITIES58, New Wanstead, London, E.11.

Letters only.New Illustrated List sent on request with

11d. stamp and S.A.E.


CHFO

OMIUM PLATINGTHE AMAT

By M. P. DAVIES

CHROMIUM plating on a small scaleis usually looked upon as a littlebeyond the scope of the amateur.

However, if the following methods arecarefully followed, quite pleasing results canbe obtained that will repay the time andtrouble taken. It must be realised that thequality of the work obtained by the amateurcannot, in general, compare with that of thecommercial plating shop.

Plating in GeneralA commercial plant may cost anything

from £2,000 upwards, and would be staffedwith highly skilled operators and technicians.The current generators would be capable ofproducing r,000 amps or more and be ofmassive proportions, while the plating vatsthemselves would be capable of containingfrom roo to 2,000 gallons of solution.

Each vat would have its own rinse tank,also of ample proportions. Massive copperbusbars would be led to the tanks andbe of adequate section to carry the largecurrent used for the plating. In the caseof chromium, every square foot (and theback of the article being included in theassessment of area) may take anything from90 to too amps. Some car radiator shellsand grilles have been known to require I,000amps.

Technical TermsWhile on the subject of current, one

should not confuse the terms currentand voltage. Current meaning the flowof electricity or its volume. A com-parable example- being the quantity ofwater which passes a point every secondon the Thames, say, compared with similarconditions on the Amazon. Voltage orpressure of electricity could be comparedwith the water rushing from a fire hose,this having a much greater pressure, butmuch less volume than a river. So, also,with chromium plating, the current may behigh, but only a low voltage would benecessary, say, 3 to 6 volts. It will, there-fore, be realised that the equipment willoffer no danger of electric shock to the user.

Actual PracticeIn actual practice nearly all chrome

work is nickel plated previously, and veryoften the nickel has an undercoat or thinflash of copper. Present-day nickel platingsolutions are the result of considerableresearch, because it was found that the earlynickel would not stand up to the rigorousconditions imposed on the plate in thechromium tank.

PolishingAn important part of the process for

producing bright chromium is that ofpolishing. Every article seen sparkling inchrome, owes its lustre, at one time oranother, to the skill of the polisher, whosemain job is to remove light scratches andblemishes found on the article as sent fromthe grinder or machine shop. These he willreplace with very fine scratches made withhis polishing " mop." These scratches

The completechromium -platingplant ready for use.

would be visible only under a lens, but thearticle would normally appear highlypolished. The polishing lathe itself is of tendriven by a 3 h.p. motor at 3,000 r.p.m.,and is usually equipped to take two mops.After the article has been nickel plated itis returned to the polisher for final polish-ing or " colouring," and is then ready toenter the chromium tank, after which it isready for dispatch.

The Amateur's PlantSmall fittings, such as nuts and bolts,

small model parts, terminals, etc., are suit -

Thin M.S. rod of sufficientlength to allow withdrawalof cylinder from solution

Thick wiretight fit

clearance

Liquidlevel

Largeclean

tin

Slidingfit

Cork

- Soldered

SolderedI(

Dimensions to suit tin CelluloidFig. I.-Sectional view of the variable

resistance.

able for the process with the equipmentdescribed below. This layout has beendevised in the simplest manner so thatreaders with the barest workshop materialsand technical knowledge may experiment.

In the first place, no nickel plating andno polishing lathe is included, but anyreader possessing these adjuncts would, ofcourse, be able to produce a more profes-sional finish.

The metals suitable for plating are the

following : steel, copper, the brasses, nickeland German silver, but not aluminium. Itwill be necessary to have the followingitems: a charged 6 -volt accumulator, aquantity of chromic acid, a little battery acid,some spirits of salts, two pieces of leadstrip, some thin and some thick baredcopper wire, and various odd pieces of easilyacquired materials. It will thus be seenthat the whole equipment is quite inexpen-sive.

Variable ResistanceThe only part of the apparatus that will

have to be made is the variable resistance,and details of this are given in Fig. r. Itconsists of a cocoa or similar tin fixed toa baseboard by means of two right-angledtin strips which are soldered to the tin, onebeing longer to take a terminal as shown.,It may be safer to solder up the seams ofthe tin as well. A vertical rod is alsosoldered on to allow a cork to slide up anddown, which operation will later control thecurrent to the plating " tank." On thecork is mounted a split cylinder of tinwhich may freely enter the cocoa tin butnot make metallic contact at the bottomowing to a disc of celluloid (see Fig. r).

The jam -jar containing the chromic acidshould stand in a container of water, suchas a tin or saucepan, mounted on two bricks,as in Fig.2, and some source of heat providedunderneath. A small spirit burner wouldbe suitable. The glass -engraved type ofthermometer is more suitable for use becausethe chromic acid would spoil the wood andmarkings of the ordinary kind. A pailwould serve as a rinse tank.

Further DetailsScrape the lead strips bright with a knife.

They are to be the anodes and, having madethe variable resistance, wire all up, as inFig. 2. Cut a piece of tin about zin. x 2in.and solder to one end a short length ofcopper wire (about 3in.) in order that thetin may be hung on the centre thick copperwire and be immersed in the chromic acid.The centre thick wire is normally called thecathode bar or rod. This square piece oftin will act as a starter to condition theanodes for plating.

Warningword of warning is needed attimelynA

this stage. The chromium process gives offconsiderable fine spray, injurious to the noseand throat. Ample ventilation should begiven while the current is on. The idealwould be an extractor fan as in large plants.The skin and clothing should also be keptclear of the chromic acid, which substance

126 NEWNES PRACTICAL MECHANICS !December, 1953

U

is liable to cause ulcers and skin troublesif neglected. Washing soda could be usedas an antidote followed by clean waterrinsing. There being some fire risk, the solidacid, particularly, should not be spilt abouton sawdust, rag, etc.

Method of OperationWarm the saucepan or container until the

temperature of the water reaches 35 deg. C.(98 deg. F.). Remove heat, and allow thechromic acid to warm up, adjust heat againuntil the acid has reached 35 deg. C. Thecylinder being out of the resistance solution,hang the tin starting plate on the centre rodof the jam -jar ; his can be done simply bybending a hook on the end of the startingplate wire.

Lower the resistance cylinder slowly intothe soda, until the starting plate gasesquietly. Allow to continue for two minutes.Meanwhile, twist some thin wire round theactual job to be plated, preferably on a partof it that will not show later, raise the resist-ance again, take out the plate and leave inthe rinse tank. Hook on the actual job asbefore, lower the resistance until there is asteady turbulence and gassing seen round thewire. Allow the plating to continue forhalf a minute only as a trial. Raise theresistance out of the soda, take out the job,and rinse well.

Resistance unit

on, but should be started up instantly theyenter the jar. The reason for this is thatthe chromic acid is apt to remove the finei:oolish before the chrome plate can protect it.This precaution is not so necessary with workthat has been nickel plated, or with steelfittings. It is sometimes a help, in the caseof irregularly shaped articles, to increase theCurrent some 5o per cent. of their normalrequirements. This " strike," as it is called,should only last for a feW seconds from thetime the article goes into the jar.

The chromium process in general has apoor electro-chemical efficiency, some 15 percent. only, and suffers from failure to platein, recesses of the article, while at the sametime " burning" the parts that stick out.

Faults That May AriseShould the article come out unchanged, or

just plated in parts, it should be stripped ofany chromium and repolished, followed withanother try, using a little more current. Ifit comes out dull grey all over, it is probablya sign of excessive current. The currentshould never be interrupted during the pro-cess of plating. Sometimes trouble is foundwith very small screws and parts, these com-ing out burnt, even with the lowest current(it is of course realised that the current isat a maximum when the resistance cylinder isright down, and vice versa. These small parts

Lead strips wide reachingto bottom. Coupling wireand wire from resistancesoldered on

Thermoiheter

The result will be known as dull chrome,as the article was not polished. When oneis confident of the procedure, plating canbe continued for three minutes, but the tem-perature should not be allowed to rise over45 deg. C. (iii deg. F.). Although no volt-meter or ammeter has been mentioned, thesecould be a help to those readers who possessthem. After the first satisfactory job hasbeen turned out by the gassing method, thevoltmeter could be put across the anodes andcentre rod, and its reading could be used asa rough guide for similar sized work, thoughnormally instruments can be dispensed with:

The job to be plated must be free frompaint, dark stains, grease and scale, but apartfrom this, no great care need be taken, whendoing dull chrome, except for a cleaning upand wipe over.

Polishing is NecessaryIf the usual bright chrome is required,

the article must be polished to the best ofthe reader's ability, wiped over with a rag,and then plated.

All electrical joints should be perfect, thecentre cathode rod should be kept clean, andpreferably damp, to assist contact.

There are quite a few snags likely tottrise,especially when articles of varying shapes areattempted. Chromium plating was neververy simple, for technical reasons alone, butthe reader will at least be able to make astart and gain interesting experience.

Polished fittings should not be left in thechrome solution,, without the current being

Burner

should be shielded, by having a wire ring chromium, with orround them to absorb excess current as in metal.

Fig. 3. As one becomes interested and gainsexperience in the work, troubles are usuallyovercome. Should larger work be in mind,everything would, of course, be increased insize and quantity, and the expense would beconsiderable. It would also be limited bythe current available.

Stripping Faulty Chromium PlateA jam -jar containing a solution of spirits of

salts 'in water, of about one to one con-centration is all that is necessary. Thefaulty part should be immersed in the solu-tion until the fizzing stops; the chromium willthen have been dissolved off. Rinse and drythe article.

Quantities of ChemicalsWhatever size jar is used, the chromic

acid solution should be madeup in the pro-portion of 5oz. pure dry acid to the pint ofwater. A trial run should be made, firstwith the starter plate, then with a piece ofscrap brass or copper. If no chromium plateappears a small addition, no more than ateaspoonful, should be made, of accumulatoracid (not concentrated sulphuric acid).

The resistance solution comprises 4oz.washing soda per pint of water, and thestripping solution should be one -part spiritsof salts (hydrochloric acid), to one partwater.

The Theory in BriefIonic migration of chromic acid takes place

as a result of an applied potential to twoelectrodes in solution, hexavalent chromiumbeing reduced at the cathode, to trivalent

Fig. 2 (Left).-Generalarrangement of the chro-mium -plating plant, showingan ordinary pail used as a

rinse tank.

Fig. 3 (Right).-How asmall part to be plated isprovided with a wire shield.Chromium jar

in saucepan.

Cathode wire or roo

Small Screwwired up andshielded

without deposition of

New Small Car in Production

The " finished" end of the 8 h.p. Standard production line at the Canley, Coventry, factory ofThe Standard Motor Co., Ltd., where the new family car is already _coming off the assembly

lines in volume production.


Telephone: MUSEUM 9594

H. FRANKS58-60, New Oxford St., London, W.C.1

One Minute fromTottenham Court Rd. Station

PORTABLE FIELD TELEPHONESETS, type D. fitted handset extra

headset, tuned buzzer. etc. 25/10/ -the pair.

STAINLESS STEEL AERIAL WIRE,gauge 7!0151n. 1,600 foot reel. Price40y- per reel.

P.O. TYPE CRADLE SWITCHES.Ref. YA11882, one change -over, onebreak contacts. 1/9 each, 20/- perdozen. 9,000 available.

500OILS- OHM. ELECTRO - MAGNETC0 Per doz.60 - 01111. ELECTRO - MAGNET

COILS, 10,000 available 01 both types,516 per doz.

1224 VOLTS HOOVER BLOWERMOTORS, Ref: 10KB:115, as recom-mended for car heaters in a recentissue. Price 27/6 each.

TUFNOL PULLEYS. Fitted ball races,external diam., 211n., internal diem.31161n., 2,9 each, 301- per doz.

DITTO. 41in. external, an. internal,5/- each. 55,- per doz. 2,000 of bothtypes available.

MINIATURE IMPULSE MOTORSmade by. " Gents " size 3 x 2 xsuitable for operating models.switches. etc. operates off 4;6v.a.c.,:d.e. and is very powerful for itssize. Price 8/6 each. post paid.

BUBBLE SEXTANTS, Type MKIX,complete in carrying case, ideal forMarine and Survey work. 25/-.

SYNCHRONOUS CLOCK UNITS.Self-starting 2001250 v. a.c. 50 cycle,fitted Sangamo motors consumption2i watts, size 211n. diam., 21n. deep,geared 1 rev. 60 mins. friction reset.Ideal movements for electric clocks.With gear train and 51n. hands. Price2216 each, post paid.BULL " 1/10th. II.P. CAPACIT.4-TOR START INDUCTIONMOTORS. 2.'5/250 volts a.c.. 50 cys.Speed 1,425 r.p.m., fin. diam. spindlereversible. Ideal for projectors, etc.£3/12/6 -each.

SANGAMO MOTOR UNITS, MODEL

0 57,.c. final speeds,

27/61 rev;

ea24 lars.- 200/250 v.

a cyclech. -

SANGAMO MOTOR UNITS. MODEL7, final speed 1 rev. per 7 days, 230/250v. a.c. 50 cycles. 30/- each.Ex -Air Min. GEAR PUMPS. Type.REP/1. made by Rolls-Royce, sizeapprox. 6 x 51 x 510. Price 30/- each,post paid.

STEP.DOWN TRANSFORMERS, in-put 180/230 v. A.C., 50 cycles, output9.2, 4.2 v., 10 amps., ideal for soil heat-ing, spot welding, etc., 85/. each.

SELECTORS, Type 10K/13045, fittedcam -operated contacts, 211n. plasticgear. 12,24 volts D.C. operated, 816each.

Ex.-R.A.F. 24 -volt CAMERAMOTORS, Type B, size 41n. x 4in. x4in.. approx. 4-h.p fitted with 3ft.flexible drive, suitable for operatingsmall power tools. 351-.111611 QUALITY ex -A. NI.VACUUM PUMPS, size 6in. x 4in.x 4in. approx. Flange mounting,weight 51b., spline shaft 2in. long Ain.diameter needs a f h.p. motor todrive same. Price 371 each.

SLIDING RESISTANCES. Enclosedtype 20 OHMS 2.3 amp. Price 221each.

HAND GENERATOR POWERUNITS. Type No. 7 ZA 17571, giving anoutput of 6 volts D.C. at 31/4 amps.,for charging. These are unused andhoused in metal cabinet 17 x 10 x 7in.,4716.

AIR-PREMaURE OPERATED CON-TACTLNG UNITS, housed In bakelitecases,'.Rel. No. 205/95.. 9/- post paid.

worAny RHEOSTATS, 71 ohms., 81amps.. 25,- each.

ALUM F;TERS. Ref. 6A/1537. Ideal forconversion to barometers. etc., 71each.

ASK- TEMPERATURE GAUGES,Ref. No. 6A 510, fitted Mercury inSteel Capillary Tube, Transmittingtype. Reading -30/0/50+ Centigrade.Suitable for greenhouses, etc., 18/6.

SYNCHRONOUS MOTORS, 203/250v.a.c. 50 cys. with gear -trains. Finalspeed 1 rev. per hour. Ex -TimeOperated Units by well-knownmakers, size 3f x 31 x ain. Price 21/6post paid.

"KLAXON." 24 Volts d.c. shuntwound 1/25th h.p. motors. 2.500 r.p.m.continuous rating, 40/- each.

RECTIFIER UNITS, input 200/250volts, a.c., 50 cycles, output 24 voltsd.c. 31 amp.. FA, each.

PREDICTOR UNITS. Fitted fourvariable speed gear -boxes, 115 voltA.C. motor, numerous worm gears,right-angle sears, approx. 78 ball -races, etc. ; weight 78 lba., cost 2300.

C 2ea11ch to make. New in original cases.each.

TRIPLEX GLASS DISCS, 91in. diam.,3,161n. thick, ideal for Port -holes,etc. 3/6 each. 40/- per doz.

CLOCKWORK MOVEMENTS fitted" VENNER " Escapement, runs 10hours one full wind, final speed 1 rev.75 secs. Price 9/. each, post paid.

" STANCOR." U.S.A. 2.5 K.V.A. 50/60cycle auto -transformers. Input,115/250 v. Output 110 v. Completelyshrouded. £11 each.

FULL MAILING LIST PRICE 6D.

IT IS SIMPLE TO

ELECTRICBLANKETFOR COLDER

NIGHTS

COUNTLESS

THOUSANDS

ALREADY MADE

AND IN REGULAR USEWith all necessary heater cable andeasy -to -follow blueprint. For 200-250 volts A.G. or D.C.601n. x 30in. im(Single bed) ev/ post free.601n. x 50in. /(Double bed) uvr post free.Blueprint only (either size) 1/6

post free.

MAKE THIS LUXURIOUS

Per personal use, or as amach -valued gift, an electric.blanket is the ideal thing.lid it's so much cheaper to

make one from the materialssupply for it. When made,

your blanket is equal in allrespects to those costingmany times more in theshops. Current consumptionis negligible and the benefitsit gives are beyond measure.Absolutely sale. Easy tomake. This blanket is aboon to health and comfort.

TEST METERFOR AC/DC

OPERATION

ANEROID BAROMETERAS SOLD FORS ens.

YOURS 5,FOR

DEPOSITflatance by monthly

payments of11/ -

or 55/- CASHA well -made and accurate Instrumentof handsome appearance and great

-sensitivity. Offered -at, half Use. usual,price. BRAND NEW and in perfectorder. Make splendid gifts.

First grade moving -Iron meter of great accuracyand robust construction. Indispensable to all whohave to do with radio. electrical circuits, etc.BRAND NEW AND GUARANTEED. Offered at

exceptionally favourable -ANIMETERS trice. 0-25 V., 0-250

0-5 amp or 0-10 Ad lmp.F.s.d. el I. v. A.C./D.C. 0-25 19/..

Postage 1/- any model. Projection mounting. 18 mA.. A.C. /D.C.

ILLUSTRATED. ELECTRICAL CATALOGUE -Send 3d. in Stamps.

MAGSTATSSPECIAL THERMOSTATS

I

ts t ARRY 1 AMP. A.C. ADJUSTABLE FROM 50-220° F. II)EAL FOR THE HOME AQUAR-

IUS'Measures only lan. x lie. x iln. TheMagstat (shown here with cover re-moved) incorporates ingenious magneticsnap action and Is fully controllable from50-220° F. Applications to which it mayhe put are very many, and a fully descrip-tive leaflet will be sent on receipt ofS.A.E. The Magstat has a Post Office

Eng. Dept. certified compliance

516of B.S.WO.Postage 3d.

When you buy from -Technical Services Co.,you buy with a difference. The bargainswe offer each month are brand-newquality lines, very favourably priced and allorders are given personal attentiorr Weinvite enquiries, and will always gladlyadvise without obligation. Please send S.A.E.for matters other than orders equiring areply from us.

HIGH QUALITY GUARANTEED

HAIR DRYERYOURS 5

FOR DEPOSIT

Balance by monthly paymeMts01 11/-.

A soundly made, brand new hair-dryer. Blows hot or cold asdesired. Has many other usefulapplications. Will give yearsof unfailin,, service. For 203/250 v. A.C. or D.C. Cash Pries 68/-1111 AND NEW AND GUARANTEED.

ERAND-NEW PRECISION BUILT

ELECTRIC MOTORSFor Use Where Ac:uraey is Essential

UN !VERSA 1. 1.C. D.C. 230/250v.BRAND NEW,PRECISIONBUILT. 3 4,1n.long x 3in. be-tween fixing cen-tres : shaft diam.dd66 in., extendinglin. 25 watts ; 6,000r.p.m. runninglight : built - insuppressor.A real precisionlob. Applicationsinclude Hair-

dryers, Drink and Food Mixers. etc.Four -blade Fan to fit them:MA.1e

.60me 2/. each. Post 6d.

THE TECHNICAL SERVICES COSHRUBLAND WORKS BANSTEAD SURREY

Telephone : BURGH HEATH 3830.

SPECIAL OFFERS'XMAS DECORATION SETS with 12lamps and 12 bell -shaped shades, very attrac-tive, wired ready for use on 230 v. 22/6. Posti.e.SCOUT SIGNAL LAMPS. 311n.. completeoutfit in case, with morse key, inspectionlamp. spare bulbs, etc., only a few left, 15/6.Post 2:-.METAL RECTIFIERS. Bridge types.6 volt 1 amp, 1041 ; 12 volt I amp, 12/6.DOUBLE READING AMMETER. -Inleather case, A.C./D.C. reading 3 and 15amps., 211n. dial, portable type, with testleads. 221. post V,AMMETER.-21in. Flush 0/25 amps.Moving Iron. D.C. 21. post 1/-.M1LLIAMMETERS.-Moving Coil, D.C.2/in. Flush 0/20, 0:200, 0250, 12/6 : 31in.

. Flush, reading 150-0-1,500, a very usefulmeter with a good open scale. 222. Post 1/-.MAINS TRANSFORMER. -200/250 volt,with output of 12 volt 10 amps., well madein metal case, 91n. x 511n. x 41n. with switch,plug, etc. 50/-, post 2/6.PORTABLE ELECTRIC BLOWERS. -220,230 volts 220 watts. Completely en-closed. 8ft. flexible hose and nozzle. 7yds.C.T.S. Flex. Many uses where clean, dryair is required. 27/101,CLOCKWORK MECHANISM. Precisionmade movement with contacts snaking andbreaking twice per second, can be used forswitching on and off lamps, etc. Brandnew in sound -proof cabinets, 120. post 1/6.'INSPECTION LAMP. -Complete withBattery Case. Fits on forehead. Leavesboth hands free. 71, Post_SEEDER COUNTER 0-9999. lin. x an. xOn. Very useful, 10/, post ed.Al EH, PUMPS. -These pumps enableyou to fl,1 all accumulators on the bench-with the carboy at floor level. Brand new,only 30,-, post 2/-.P.M. SPEAKERS., --In cases. Ideal forextension speakers, 61in., 30/- 5in., 17/6.postage 2:-.THERMOSTAT SWITCIL-Bimetal typein, sealed glass tube, 21in. x On. 30 deg.

- Cent. Ideal for Aquariums, Wax and OilBaths. Gluepots, etc. Will control 1 amp.at 290 v., 5,- each, post 6c1.TDERNIOSTAT.-Satchwell 121n. stem.,0,250 v. A.C.,D.C. 15 amps. A.C., .1 amp. D.C.10 to 90 deg. Cent., 35/, post 1:6. -

ELF" CIRCUIT BREAKER, avoidsblowing mains fuses if circuit is overloaded.-Reset In an instant. Very useful on testbenCh. Size 31n. round. 9/6, post 1:-. .

LOW VOLTAGE CIRCUIT TESTER.-A self-contained unit for reeking acomPleteand rapid check of the generator battery.circuit of a vehicle. Battery voltage, reg-ulator and cut-out settings and generatorperformance can aR be easily determined.American made. Complete with instructionbook. 2540.0. post 2/,BATTERY -TESTER.-Complete in case

-..with heavy current- test. prods 200 amperes..Plate selector switch with 7 positions,enabling the test to be made In accordancewith the number of plates per cell. Meterwith coloured scale indication, 70/-, post2/-.HAND GENERATOR or Battery Charger.-2 volts D.C. at 4 amps. contained in astrong metal- case with automatic cut-outvery useful where no mains are available,could be converted to a wind charger. Only39, carriages/-,BALL RACES. -No. EE2, fin. x lin., 3/-,

.301-doz.. post free.THRUST RACES. -13/161n. x tin.. 1/8,post free:VOLTMETERS. -0-300 A.C. Moving Iron3/1.n. Flush or Surtace Type, 25,-; 0-300Flush D.C. Moving- Coil, 10/6 0-29, 2in,mesh Moving Coil, 7/6-; 0-40 2in. Flush

1048: post 1/-.BATTERY CHARGER " WESTALTTE."Input 1001250v. A.C. Output 12 v. 16 amps.,variable metered output, fused. worth £34.Our price while they last. £15. Carr & Pkg.15/-.ACCUMULATOR CIIARGERS, 230 v.A.C. in black crackle case with fuses andmeter, 6 and 12 volts at 4 amps. BargainPrice. £4.1916. Pkg. & carr.. 5/-.RECTIFIER UNIT, P.O. type. Input200/250 volts A.C. Output 50 volts 0.75 amps.,D.C. Westinghouse. 201, carriage 10/ --RECTIFIER UNIT. -input 230 volts.Output 12-0-12 volts 1 ampere, 50:-. Packingand carriage, 5/-sPORTABLE TEST METER --Just thejob for the home constructor. In neat case,61n. x Sin. x 9in., reading 1.5, 3, 150 volts, 6and 60 m,A D.C. 5 k. and 25 k. ohms, 25/ -each to clear. Post 116.SLOW MOTION DIALS. -61n. Scaled0-100, reduction 200 to 1 or direct ideal forwa.vemeters. signal generators. Its. Ourprice, while they last, 5/6. post 1.-.FLASHING SNITCH UNIT with 6 con-tacts. Full rotation 60 seconds, operatedby a Sangamo Synchronous Motor, 230volts. A.C. 2 watts. In metal case. 3in. it2lin. x 2An. 15:-. post 1,-.SW ITCH ES. -A row of 5 in a flush mount-ing Bakelite moulding 51in. a Ole. x .21n.Ideal for model railways, etc., 56, post 9d.24-1'OLT MOTOR with reduction gear andcam -operated contacts, 158. post 1/-.24 -VOLT D.C. MOTORS with double endedshaft 2in. x 3in., 8/8. post 1/-HAND TELEPHONE -Brand new withcord, 15:- each, post 1/6.VOLTMETERS, CELL -TESTING. -3-0-3volts Moving Coil D.C., complete with testleads !n Leather case, 35/-, post It-.CUTTER READS. -Recording high impe-dance. A bargain at 55:- each post 1/-.CUTTER STYLI!, 4/- per doz., large quan-tity available at special rates.

Comprehensive List Now Ready 611.

WILCO ELECTRONICSDEPT. P.M.,

204, LOWER ADDISCOMBE ROAD,CROYDON.


RADIO TELEPHONESBrand-new transmitter/receiver. 53-75 me/s. Visual range. Completein canvas carrying case and in-dividually boxed in heavy transitcase. Works off set of dry batteriesor a vibrator from a 12 -voltaccumulator. Batteries or thevibrator stow inside the unit.Supplied less batteries and vibra-tor at Special Price of £9.17.6 or£18.17.6 a pair. Carriage 5/6each. Vibrators 37/6 each.

VALVESSALE PRICE 8/9 EACH

35Z4, 10P13, 20D1, 20F2, X66, 1S4,155, IRS, IT4, EF9I, IOFI, 6E15,EL9I, L63, UAF42, X 113, X143,DN143, PZ30, EF39, 6K7. EAF42,ECC9I, UM4, ERA 6A8, I2K8,3V4, 807, 501.6, 616, 3834, 6Q7,EF36, 6SA7.

T.V. TUBES. Personal callers only.Picture shown on each one. Mostmakes. 9in., £3 ; 10in. and I2in., £5 ;

!Sin., £6. Have been used for testpurposes only. Post orders acceptedfor 2I in. projection tubes, slightfaults but brilliant picture. Price2.5,4, post 1/6.

C.O.D.or

C.W.O.

RADIOGRAM CHASSIS. Brand new 1953 show models. Originally designed for the

export market, and exactly as fitted in radiograms costing over £100. It has six wave-

bands, and a six -position tone control. All knobs engraved, negative feed -back, and

fly -wheel tuning. 11-115 metres in five ranges, and medium wave 188-550 metres.

Our special PRICE £15.15.0, carriage 4/6. Also the home market model with long, medium

and short bands. Gram. switch position and pick-up sockets. Our PRICE £12.12.0,

carriage 416. Both chassis measure I llin. x 7in. x 8in., and with valve line-up 6E3E6,

6BA6, 6AT6, 6BW6, 6X4 Modernise your set now.

EXTENSION SPEAKERS. Brand new 61in. P.M.low impedance speakers, mounted on polished and veneered baffle a! modern design.Gold sprayed metal fret fitted. 5 feet of lead ready connected. GIFT PRICE 19/9. Post 1/9.WIRE. In sealed tins, nickel -chrome, with special run -out mechanism. 50 yards (.014in.) and 25 yards (.032in.). 4/6 per tin. Also spring steelin same sizes at 1/-, post 4d.AMPLIFIERS. Brand new (ex W.D. unused). Contains EF36, 2 transformers, 400 ohm relay, volume control, various condensers, resistors,etc. Case measures Sin. x 5in. 9/6, post 1/6.AERIAL RODS. Copper plated steel, I2in. long. Ex 19 sets. Interlock to any length. 2d. each, Post 6d. on I dozen.TELESCOPIC MASTS. Ex W.D. but unused. Extend to 7ft. 6in. Base diameter yin., tip Closed length 15in. Ideal aerial. GIFTPRICE 7/9, post 1/3.

INSULATING TAPE. New and wrapped, fin, wide, '.lb. rolls. Listed at 3/6. OUR PRICE 1/6.TUNING CONDENSERS. Two gang. .0005 mfd., standard size. Store soiled, but all tested. CLEARANCE OFFER 2/9, post 9d. BARGAINof 3 for 7/-.O.P. TRANSFORMERS. CLEARANCE OFFER at 1/9 each. Post 1/-. Will match all normal O.P. valves to 2-5 ohm speech coil.INDICATOR UNITS. Ex W.D., but brand new condition. Valves and C.R. tubes removed but otherwise complete. Units includeindicators type 6C and type 62, power unit 657 and C.R. unit design L. Price 12/6 each, carriage 4/6.FUSE HOLDERS. Porcelain. 15 amp. MEM, Kantark Minor (brand new). Complete with fuse, backwiring type, 250 volts. TO CLEARat 9d.. post 4d.ALUMINIUM SHEETS. Brand new. 3 metres x 2. 27 S.W.G. 27/6, carriage 2/6.METERS. Ex W.D. but unused. Accurate 100 micro -amp. movement. tin. scale in 2lin. square mounting. BARGAIN PRICE 27/9, post 1/3.USED, 12/9.

MICRO -SWITCHES. Latest American midgets. 230v., 3 a., lie. x (in. x Ilin. BARGAIN OFFER, 3/6.CRYSTALS. Brand new Germanium crystals, by B.T.H. Long wire ends. 2/3, post 6d.MICROPHONE TRANSFORMERS. Ex W.D., but unused and brand new condition. In fully shielded case. 3/9, post 9d.PICK-UP TRANSFORMERS. New and unused. E.M.I. type. Fully shielded. 3/9, post II-.

STAMP FOR COMPLETE CATALOGUE

DUKE & Co., 621, ROMFORD ROAD, LONDON, E.I2GRA. 6677

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YOU, like them, can find SUCCESS'

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ELECTRICAL ENGINEER"Thank you for `The BennettCollege Diploma'. The Elec-trical Engineering Course' hasbeen an excellent investment,which not only gives me asound knowledge of ElectricalEngineering, but also of Mathe-matics ... On enrolment, I hadnot the slightest knowledge ofany form of the Course . . .

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* All these letters, and thousands of others like them, may be seen on re-quest at The Bennett College, Sheffield. To comply with the College'sstrict policy of complete privacy for every student and graduate, fullnames have not been shown, and for the photographs models have been used

WHATTO DO There are overa hundred different Bennett CollegeCourses. Whichever one you take, youwill receive the personal attention ofpicked tutors. Choose your subject fromthe list of courses and tear out the coupon.Send it off now. You will receive theappropriate College Prospectus.Choose the course you needAgricultureArchitectureAircraft MaintenanceBuildingCarpentryChemistryCivil EngineeringCommercial ArtDraughtsmanshipElectrical EngineeringElectric WiringEngineering DrawingsFire EngineeringForestry

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R.D.C. is largely due to the thorough,painstaking and individual tuition Ihave received in respect of this course."(Final Exam, of the Institute of Quan-tity Surveyors.) " I have recommendedit to my assistant and he has now en-rolled with you." W.O., Warrington.

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Lfa Please write in block letters.

December, 1953 NEWNES' PRACTICAL MECHANICS 129

LETTERS1° 1HL EDITOR

The Editor does not necessarily agreewith the views of his correspondents.

Prism Binocular Adjustment

SIR,-Yourreply in October's PRACTICAL

MECHANICS to Mr. R. Robinson con-cerning double images in a prism binoculardeals only with the least likely cause of thetrouble.

You are quite correct in stating that .doubling is due to lack of parallelism in theoptic axes, and all prism binoculars incor-porate some means of adjustment of theseaxes. Most commonly it is achieved by slid-ing of the prisms longitudinally on their seat-ings, and in the better makes of instrumentthis is usually controlled by four adjustingscrews in each body, bearing on opposingfaces of the prism cover plates, their slottedheads being concealed by the leather coveringof the instrument. These screws also serveto retain the prisms on their seatings, andobviously one must be backed off a triflebefore its opposite number is screwed in.Excessive tightening must be avoided.

Some cheaper binoculars do not haveexternally accessible adjusting screws, theprisms being held on their seatings by springleaves engaging in slots in the body interior.Adjustment is carried out by assembling theinstrument without the endplates, the prismsthen being accessible through the ends of thebody. After adjusting, the prisms arecemented in position and the endplatesreplaced.

Another type of adjustment, sometimesmet with in good -class instruments, is forthe O.G.s to be mounted in double eccentricrings, by means of which their opticalcentres can be offset in any desired direction,the prisms in this case being mountedimmovably.

For a binocular to, be properly collimatedthe optic axis of each half must be trulyparallel to the mechanical axis of the centralhinge, as only in this condition do theyremain parallel to each other throughout thewhole range of eyepiece separation. This isextremely difficult of achievement for anamateur without proper testing equipment.

If, however, the owner is only concernedwith adjusting the instrument for his ownparticular eye separation, this can be donesufficiently accurately by the followingmethod. Some provision for the firm clamp-'ing of the binocular is essential.

With focusing adjusted and eye separationset to the user's P.D., mount the binocularin the clamping device and direct it at adistant well-defined object, such as theextreme tip of the neighbouring churchsteeple.

Look through the R.H. telescope with theleft eye, and at the same time observe thedistant object with the right eye. Adjust thebinocular bodily until the magnified imageseen by the left eye is perfectly superimposedover the target seen by the unaided righteye. A little practice is necessary to ensurethat the operator's own ocular convergence isnot called into play.

When the two images are perfectly super-imposed, clamp the binocular firmly, andcheck to ensure that the clamping has notdisturbed the setting.

Now look through the L.H. telescope withthe right eye, and observe the target directly

with the left eye. If adjustment is neededthe two images will not -be superimposed andthe optic axis of the L.H. telescope must beadjusted by whichever system is provideduntil they are. Patience is necessary, and anoccasional check through the R.H. telescopeto ensure that the binocular is not beingmoved bodily during the adjusting operation.

When adjustment is carried out by thissystem it will satisfy the condition that theoptic axes are reasonably parallel for the oneparticular user, though they may not beso if the binocular is used by a person ofgreater or lesser eye separation. Completecollimation so that adjustment is correct forall users is a job for the fully equippedexpert.-F. TAYLOR (Stonehouse, Glos.).Space TravelSIR,-Re your leader in the October issue.

It is a mysterious thing that the peoplein whom one would expect to find plenty ofimagination are so strangely lacking in it.As accomplished men of science they think,perhaps, that it is fit and proper that theyshould appear dignified and aloof. If they" let themselves go " they are afraid of beingregarded as " woolly minded." Let usaway with this stupid inertia and look atsome facts. The famous American astrono-mer, Simon Newcomb, was franklypessimistic as to the feasibility of heavier-than-air flight. Sir Joseph Banks could seeno future in steam at sea. Possibly Banksfancied himself as a marine expert, for werecollect that he accompanied Captain Cookon his first circumnavigation of the world.

True, Banks was not an engineer he wasa naturalist ; in this line he had plenty offoresight arid vision, and many of the botani-cal gardens in different, parts of the worldowe their origin to his personal energy. Inhis later days he became President of theRoyal Society, and in this capacity he musthave made acquaintance with many eminentengineers. Perhaps this explains why heshowed good prescience in co -related matters.He was, for instance, a staunch patron of theswitch -over from oil -illumination to gas. Inthe application of steam at sea, the celebratedDoctor Lardner was unable to see quite asstraight as one might have expected in a manof his attainments.

Again, he was a frigid spectator in talkson the proposal for a certain trans -oceancable.

Lay one on the bed of a river and, pos-sibly, across the Straits ' of Dover-but theAtlantic L-P. BOWN (Northampton).

Wimshurst MachineSIR,-I was interested, in Mr. R. E. C.

Davies' comments on small Wimshurstmachines appearing in your August issue,and I thought the following might interesthim.

I have in my possession a minianire Wims-hurst machine which 'my father made in1906. The plates are of ebonite, 3in. dia.and 3/32in. thick; and have 16 tinfoil sec-tors. In place of brass balls the conductorsare made of. " Sparklet " soda water syphonbulbs mounted on varnished glass rods.Some time later he added little Leydenjars made of specimen tubes.

When made, the little machine, if warmand dry, would excite at once, giving asteady stream of fin. sparks and would lightfour 4in. vacuum tubes. It would chargesmall Leyden jars giving quite a smart shock,and carry out the usual experiments.

The machine would also drive a littlestatic motor, something like a horizontalWimshurst machine, which he made to adescription published about 1912.-G. N.GEE (Kidderminster).

Magnetic Door Catch : Dynamo BulbsSIR,-Re plge 524 of PRACTICAL MECH-

ANICS for September: Magnetic DoorCatch, I am afraid your reader will findthat his magnet will not remain permanentfor long if the plate actually touches themagnet when the door is closed. It shouldbe arranged so that there is a sliding actionoff the poles.

With regard to Icarus's remarks on page 5of THE CYCLIST in the October issue, I haverecently fitted a dynamo set to my cycleand I mounted the lamp (which is on thefront fork) on a tin. wide rubber bandover which I clamped the lamp bracket.This avoids excessive vibration, which musttend to shorten the life of the bulb.-K. N.HOWARD (Emsworth, Hants).

" The Obedient Dog "SIR,-With reference to the electrical

novelty " The Obedient Dog," in theSeptember issue, the mechanism described

seems very wastefulon battery current.

By reversing theelectrical action, i.e.,using the battery to -

release the dog ratherthan hold it in itskennel, the battery isonly in use for a frac-tion of a second.

This modificationmay easily be effectedby the use of a smallpawl which will holdthe propelling arm inposition. The electro-magnet is then usedto pull the pawl awayand thus release thepropelling arm. Thesimple arrangement isshown in the accom-panying sketch.

Of course, withthis set-up the contactstrip should :lottouch the conta:ctstud as described inthe article, and shouldonly make when the

is called.-A READER (Surbiton).

Propellingarm

Lightspring

Pivot

Soft ironarmature

Electro magnetModificationto " Obedient Dog"

mechanism.

dog

An Orbital Cosmos

SIR,-Withreference to Mr. Ellwood's

article " An Orbital Cosmos," thereis no need to propose an orbital cosmos inorder to explain the red shift. A staticuniverse will do ; the shift toward the red

being considered due to a loss of energy inthe radiation covering the great distances ofspace, the greater the distance the greater theloss. It is not the red shift which rankles,but the stupendous velocities associated withthe shift. I personally am not satisfied withthe expansion, concept, but I would hesitateto settle for an orbital cosmos which retainsthe high velocities.

- The discrepancy between star ages anddistance of nebulae from the centre of sup-posed expansion is now to some extentreconciled by the new size of the universerecently put forward.

1 3 0 NEWNES PRACTICAL MECHANICS December, 1953

Finally, evidence suggests that the knownuniverse is spherical in form, and while itis difficult to say what form the ultimateuniverse will take since it is not visible, thereis no suggestion that the nebula' are in alenticular form moving about a perihelionposition. Incidenlally, perihelion is used ina wrong sense here ; we should coin a word.I suggest pericosmion.---FRANK W. Cousins(Greenford).

Writing on Lantern SlidesSIR,-Re query from Mr. S. G. Moore

(Co. Durham), Queries and Enquiries,October, the usual way to prepare acinema slide is, if white letters on blackare required, to paint the glass with men-tholeum or some other water paint, evenwhitewash, but care should be taken to avoidlumps. White is preferred to reflect the heatif high intensity light is used. Allow to drythen draw guide lines lightly with a softpencil and write with a skewer.

If black letters on white are preferredplace a piece of Cellophane between two car-bons and type as required ; afterwards placeCellophane between two glasses and bind withpasse-partout. Avoid touching printedmessage as it is likely to wipe off on the sidetouched and reduce the density.-L.TEARINGTON (Pinner).

Pocket Hand WarmerSIR,-In reseonse to J. F. Ford's inquiry

in the October PRACTICAL MECHANICS,I should like to describe a gadget ofJapanese manufacture which came into mypossession in Germany during the war.

1111111111Lid with

ventsAsbestos

shredded andbound with thick

co .per wire

Element inholder whichfits tightly,over raised

flange

Containerf lied with cotton

wool and saturatedwith petrol as with

a lighter

Mr. R. Gower's pocket hand warmer.

The container should be of convenient sizeto fit the pocket without being too tight.The element holder should fit tightly on theflange and the asbestos must not be boundtoo tightly with the copper wire.

Ignition is by means of holding thewarmer with the element up against a glow-ing ember and it will not light with a matchor similar means.

The action is that the petrol vapour causesthe asbestos to glow, which in turn heatsthe copper wire, the hot air then passingthrough the vents in the lid, to the benefitof the user. The element will last for aboutthree months, when a new one should bemade. The " warmer " will keep hot forabout 6-8 hours.

There was also another very good butsimple idea which I saw on a German armymotor -cycle, and this was two flexible tubes,

with one end fixed into the exhaust pipes(near the cylinder port) leading up into apair of " muffs " ; the end inside the handle-bar muffs was, of course, closed.

The exhaust gases passed up the tubesand the inside of the " muffs " was quitewarm. No gloves were needed.-R. GOWER(Worthing).

A Blowpipe for BrazingSIR, With reference to the article in

PRACTICAL MECHANICS, September,1953, issue, " A Blowpipe for Brazing," byP. Screaton, in the first paragraph it men-tions all that is required are a vacuumcleaner and a domestic gas supply. May I

FlexiblePipe

Fig. i.-A non -return valve fitted in a gassupply pipe.

point out that there would be an elementof danger in using this tool unless a non -return valve is provided in the gas supplyto flexible gas pipe, as indicated in Fig. 1.

Without this valve being fitted there is achance of causing an explosion and fire.

The air supplied to blowpipe is at a pres-sure of Iouin. of water, and can be increased.

Inlet

& \,%S.\

9.S .P 7fireads Valve seating

valve

Outlet InletInlet

Fig. 2.-Section and details of a non -returnvalve for gas supply.

The average gas pressure is sin. of water.If, for example, the gas opening was

blocked by a piece of coke or cinder, theair pressure being greater than gas pressurewill flow into the gas installation and viagas meter into the mains.

Air and gas mixed is an explosive mixture.Anyone lighting a burner anywhere on theinstallation will light the explosive mixture,causing flame to fire -back to the meter caus-ing an explosion and fire.

This is not what might happen, but hashappened many times in factories, and iseasily done when using hearths or cinders.

So as a safety measure for stopping thishappening the non -return valve is fitted.

I believe people using gas and air in thismanner are legally obliged if required bythe gas undertaking of their area to fix orhave fixed a non -return valve which will pre-vent air entering gas service pipes and mains.

There are several types of non -returnvalves, and one type is shown in Fig. 2,which indicates the action of the valve instopping air getting into the installation.-P. MAGUIRE (Southall).

Outlet

Stencil CuttingSIR3-1RACTICAL MECHANICS has devoted

a considerable amount of spacedescribing stencil cutting, but the latest

development has not been mentioned. Anelectronic stencil -cutting instrument has beenperfected by Messrs. Roneo, Ltd., givingresults not possible by the photographicmethod. Half -tone originals can be faith-fully reproduced and duplicated on the stan-dard machine. The cutting machine remindsone of the pictures -by -wire machine. Theoriginal to be copied is wrapped round aslowly rotating cylinder with a carbon -coatedstencil wrapped round a second cylinderwhich revolves with the first.

An electric eye is made to traverse theoriginal, and its impluses control the inten-sity of an electric spark which traverses thesurface of the stencil. This spark actuallycuts the stencil and its intensity decides thedepth of cut.-E. J. RABE (London, W.7).

Bending PerspexSIR,-Bending Perspex and similar sheeting

presents few problems until the anglebecomes sharp, as for instance a right-anglebend required when making boxes, inspectioncovers for switchgear, and so on.

An ordinary cheapwheel -type glass cutterwill do the trick (not adiamond). Cut on insideof bend, not too deeply-but just sufficiently to

provide room for the inner side of thematerial to compress in. Then plunge innear -boiling water and bend round a woodenformer.-B. FREESTONE (Akeley).

l'IlL-Persper" cuthalfway throbefore bending

Bromide Printing MediumSIR,-In reply to Mr. T. 0. Edwards,

London, S.W.9, I suggest that hecontacts H. Silverstone, 20, Oxford Road,Manchester, t. This firm's summer cata-logue, 1951, lists the following : AluminiumBromide : This is ordinary photographicmaterial, but has the bromide emulsion onaluminium base instead of paper base.Normal grade, 9i x 91. Price tos. perpacket of one gross, post is. This is exposedand processed in the same manner as standardbromide paper, and appears to offer the idealsolution to the problem.-H. GREGORY(Sheffield).

0014How to Fly. By Laurence C. Bagley.

Published by Blackie and Son, Ltd.94 pages. Price 7s. 643. net.THE subject of flying is of particular

interest to every young man to -day,and in this interesting book the authorpresents to the reader an explanation of thewhys and wherefores of flying in simplelanguage. Intended for young traineesunder instruction, the reader is told exactlywhat to do, and why. With the aid of numerousline drawings and coloured plates, the textis fully explained.

Making Pottery and Glassware in Britain.Published by Scott Greenwood andSon, Ltd.,83-86, Farringdon Street,London, .C.4. Si pages. Price 6s. 6d.,or post free 7s. zd.MOST people have a love for beautiful

china and glassware, and this book, thechapters of which . were originally writtenfor the benefit of salespeople, explains thedifference between china and earthenware,and cut glass and pressed glass. It alsodescribes the production of decorated chinafrom raw clay, and of cut glass from sand.The various processes are illustrated by veryclear half tones. Readers interested in thesubject, apart from those engaged in thetrade, will find this a very fascinating andinstructive book.

READERS' 2.'21In AHD WAH2124The pre -paid charge for small advertisements is 6d. per word, with box number 1/6 extra (minimum order 6,-). Advertisements,together with remittance, should be sent to the Advertisement Director, PRACTICAL MECHANICS, Tower House, Southampton

Street, London, W.C.2, for insertion in the next available issue.

SITUATIONS VACANTThe engagement of persons answering these

advertisements must be made through a LocalOffice of the Ministry of Labour or a scheduledEmployment Agency if the applicant is a managed 18-64 inclusive or a woman aped 18-59inclusive unless he or she, or the employment,is excepted from the provisions of the Notifica-tion of Vacancies Order 1952.

METHODS PROCESS PLANNING-4-v1 ENGINEERS required by a largelight engineering company on thesouth coast engaged on batch pro-duction work ; sound general know-ledge; good opportunity for rightman. Applications will be treatedconfidentially. Staff pension schemein operation. Box No. 111, c/0PRACTICAL MECHANICS.

FOR SALETRANSFORMERS DESIGNED and

supplied for all requirements,Trains, Welders, Television, etc.Write or phone your requirements toF. W. Whitworth, A.M.Brit.I.R.E.,Model Dept., Express Winding Co.,333, London Road, Mitcham. (MIT.2128.)

TRANSFORMERS, Rectifiers, Voltand Ammeters, Controllers, Cut:

Uouts, Battery Chargers, Power nits ;lists ; s.a.e. Harry Gilpin, Manu-facturer, Portobello Works, Walton -on -Naze, Essex.

PERSPEX for all purposes, clear orcoloured, dials, discs, engraving.

Denny, 15, Netherwood Road, W.14.(SHE. 1426, 5152.)/VETS, BOLTS, SCREWS, Rivets,

Washers and hundreds of otheritems for model engineers and

' handymen. Send now for free list.Whiston, New Mills, Stockport.

COMPRESSOR EQUIPMENT,1-.1Mis-cellaneous Items; catalogue, lid.Pryce, 157, Malden Road, Cheam.

COMPRESSORS for sale, 3 CFM,1801bs. sq. in., on metal base,

with driving wheel and receiver,price £3 ; h.p. Heavy Duty Motors,price £3 carriage forward. Wheel-house, 1, The Grove, Isleworth,(Phone : Hounslow 7558.)

HACKSAW BLADES, genuine sur-plus by leading Sheffield manu-

facturer ; 12 Blades, 10in. and 12in.'3/3 ; 24 blades, 6/-, post paid.Sawyers Ltd., 115, St. Sepulchre Gate,Doncaster.

PICADOR " ROTOSAW. Portablecircular saw attachment for

your electric drill fitted with 4in.circular saw blade, adjustable fenceto cut up to lin. in depth, ideal forwood, plastic, or soft metals ; 33/-,each, post paid. Lambs -wool polish-ing Bonnets, 5in., 4/3 each ; RubberBacking Discs, 5in., complete withkey, 4/6 each ; Abrasive Discs, 51n.,6 assorted grades, 2/-. Send 21(1. forlists of Saw spindles, Vee Pulleysand Belts, PlumMer Blocks, etc.Sawyers, Ltd., St. Sepulchre Gate,Doncaster.

CIRCULAR SAW BLADES, superiorquality, Sheffield made, 4in. 8/6,

6in. 13/6, 7in. 18/9, 8in. 18/9, 101n.25/6, 12in. 31/6 ; all post paid.Please state size of bore and teethper inch. Sawyers Ltd., 115, St.Sepulchre Gate, Doncaster.TYLER Spiral Hacksaw Blades cut

in any direction at conventionalhacksaw speed without turning thework. 10in. Hacksaw Blades 4d. eachfrom leading tool dealers. Write toSpiral Saws, Ltd., Trading Estate,Slough. for details.

HOUSE SERVICE METERS, creditand prepayment ; available

from stock. Universal Electrical, 221,City Road. London. E.C.1.

ANTI-RADAR STRIP DISPENSERUNITS. These comprise two

I/20th h.p. 24v. shunt wound motors,with train of gears, both 25 and 50to 1 reduction. The unit is mountedin an aluminium chassis and consistsof over 100 gears, pinion shafts, etc.,of the Meccano pattern, with variablespeed switch and indicator light,bag of spares, and electricaldiagram. These are all new and inoriginal waterproof packages. Theyare something entirely new andnever been offered before. Price 30/ -each, carr. paid. H. MIDDLETON,639. Abbeydale Road. Sheffield, 7.IN TWO HOURS you can sew an

Emello Electric Cord to yourown blanket ; no connections tomake, you just have to sew ; ex-tremely efficient, safe and guaran-teed 2 years ; 75 watt warms 45in. x39in., 28/- ; 100 watt, 49in. x 47in.,35/- ; post paid. Emello (London)Ltd.. Kempshott, Basingstoke.

QYNCHRONOUS CLOCK MOTORS" with gear wheels attached, 230v.A.C. S/Ph 50c., 12/6 each, plus 1/ -postage. Universal Electrical, 217,City Road, London, E.C.1.

PLATED Nuts, Screws, Washers,Bolts, Soldering Tags, Hank -

bushes, Self -tapping Screws, Grub -screws, Socket -screws, Wood -screws ;large quantities or gross cartons.List sent post free. Sinden Com-ponents Ltd., Dept. E., 117, Church -field Road, Acton, W.3. (ACOrn8126.)POWERFUL 24 -VOLT GEARED

MOTORS, series wound, will runon A.C. or D.C. ; 24 -volt intermittentrating ; final speed approx. 75 r.p.m.;weight 3llb., size 4fin. x 2iin., approx.

h.p. ; light, powerful and compact ;ideal unit for food -mixers, hedge -cutter, etc. Makers, Dumore Co.,U.S.A. ; spur and gunmetal worm -wheel totally enclosed ; price Z1/10/-,post paid. H. Middleton, 639, Abbey -dale Road, Sheffield, 7.

BLECTRIC - WELDING PLANT.-Large selection of new, surplus

and secondhand plant. Arc Weldersfrom 220 ; Portable Spot GunWelders, £28 ; Carbon Brazing and.Welding Sets (mains operated),25/15/-. Send stamp for cataloguewith prices. Harmsworth, Townley& Co., 1, Brook Road, Manchester, 14.(RUSholme 3003.)

AMAZING DEVICE, cuts perfectdiscs, wheels, etc.,to 121n. dia-

meter, with any circular, saw, 10/6 ;p.pd. ; sample gin. mahogany disc,

fit°, details, 1/6. Below:-OW TO RE -WIND and Service

Electric Motors, Generators.Complete Practical Book only 3/- ;p.pd. Below:-

HOW TO MAKE IT BOOKS:11 Whittling in Wood ; Inlay Pic-tures, Marquetry ; American ActionToys ; 21 Lovely Lamps ; 3/- each ;p.pd. Below:-BUILD YOUR OWN PHOTO Equip-

ment,-v-0 12 designs in two books.Enlargers, printers, dryers, timers,etc., 6/- , p.pd. Below:-.4.(11 POWER TOOLS You Can MakeI, from scrap, pipe fittings, etc.This amazing book of plans for cir-cular saws, lathes, band -saws, jig-saws, planes, tapping attachment,jigs, etc., has sold 250,000 copies, andis a " must " for every home work-shop, 12/6 only ; p.pd. Below:-

AMERICAN BOAT BUILDERSAnnual ; 28 boat plans, 8-22ft,

and other helpful articles, 7/6 ;p.pd. Below:-CIARBODY REPAIRING. CompleteA B C course ; illustrated ;7/6 ; p.pd. ; lists free. A.P.S. (P),Sedgeford, Norfolk.GINS. DIA. ASTRONOMICAL TELE-

SCOPE KITS, 50 x , simpleassembly ; efficient instrument easilyprepared within few minutes; self -adaptable parts, fits any 2in.0/dia. tube ; comprising : selected50mm. dia. objective at 40in. focus,. mounted in special cell incorporat-ing front glare shield recess, rearself -aligning shoulder with precisionsensitivity and correcting stop (en-sures achromatic stability with sharpinverted image), lined eyepiece focus-sing holder, turned brass eyepiecefocus, fin.. magnification 50 dia-meters (equivalent 2,500 x area-shows lunar detail, Saturn's rings,etc.), with large explanatory draw-ings detailing simple altazimuthmountings, notes, etc. ; signed cer-tification of test ; pride 49/6, regis-tered postage packing, 2/6 ; extra80 x eyepiece, fin. focus. 25/-, post6d. The following made to order :Prepared Principal Tube, aluminium,2in. 0/dia., length 38in. (assembled40in.), double camera black interior,fitted with glare stops, etc., price 45/-,carriage 3/6 ; complete Telescope,assembled, price 94/6, carriage 3/6.Below:-POLARIZING KITS, a ss or ted

laboratory grade screens forsimple adaptation to any size astro-terrestrial Telescopes, microscopes,cameras, projectors, etc. ; suitablefor astro-daylight observation, micro-scopic analysis, colour and cloudphotography, 3D cinema viewing,etc., including experimental, speci-mens, photo -elastic ' U," etc., show-ing chromatic and interferenceeffects ; with illustrated instructionsdetailing half- and full -wave experi-ments, application, etc.. price 15/ -box, post 6d. J. K. M. HOLMES," Scientific Instruments," Dept.PM3. " Vizcaya," Wolveleigh Terrace,Gosforth, Newcastle -on -Tyne, 3.

VLECTRIC BLANKET; make yourown in 5 minutes ; we supply

the interior element complete, 6ft.long, 2ft. 6in. wide, and 9ft. of flexattached ; tested and guaranteed ;35/-. Dept. E.L., Brace, Dairy Green,Thaxted, Essex.

CONSTRUCT YOUR OWN REFRI-GERATOR."-This book, written

by a refrigeration engineer, isprofusely illustrated with drawingsand photographs and tells you, notonly how to construct a cabinet orbuilt-in refrigerator, but illustratesmany that have been built byamateurs and are operating satis-factorily ; 3/9, post free from :Robert C. Scutt, Refrigeration Engin-eer, 52, Hadley Way, London, N.21.

,`/RINGERI ROLLERS to order,v wood or rubber; s.a.e. for details;

1 week. Wringer Hospital, Sandy -gate, Burnley, Lancs. Eat. 40 years.TOOL BARGAINS : High - speed

Drills, 24 assorted, up to fin.,for 17/6 ; Surface Plates, finished toline limits, 12in. x gin., 40/-, c. and p.4/- ; 50 -yard Rolls Fine Twill Emery,2in wide, 15/-, p. 1/- ; Needle Files,assorted, 12/- doz. ; fin. H.S.Reamer, 4/6 ; Hand -drill, toclear 9/6 each. Send 6d. for specialbargain list of tools to Mibro Equip-ments, 65, Knaresborough Rd.,Harrogate.

ELECTRICALBROOKS 3 h.p. Motor, 230v., 50c.,

single-phase, 2,800 r.p.m., ball -bearing ; ideal for driving wood-working machines ; latest type, inmaker's sealed box ; brand new£8/15/-; carr, paid. Blood, ArchStreet. Rugeley, Staffs.

BARGAINS FOR ELECTRICIANS.-Brand new Cables in 25-100 yd.

lengths ; T.R.S. twin, 1/044, 42/- ;3/029, 60/- ; 7/029, 95/- ; 3/029 withearth, 72/6 ; 7/029, with earth, 117/6 ;P.V.C. twin, 1/044, 38/6 ; 3/029, 56/-

'Transparent Flex, 14/36 twin, 17/6.All per 100yds. ; carriage paid.Fully wired Ballast Units, 38/6:c.w.o. ; request list. Jaylow SuppliesLtd., 93, Fairholt Road, London.N.16. (Tel.: STAmford Hill 4384.)1/ 200-240v., A .C.ELECTRIC

MOTORS," , fitted withEft. flexible shaft drive, 0 -}in. chuckArbour 3in. grinding wheel, wirebrush, spiral wire brush and polish.ing mop ; complete Polishing, Grind-ing and Drilling Set , £3/2/6 ;carriage and crate 5/- extra. Wilton,92. Toynbee Road, Wimbledon,S.W.20.

MODEL DEALERSLONDON. - Robson's Hackney's

Model Shop, 149-151, MorningLane, E.9. (Tel.: AMHerst 2989.)

HOBBIES LTD. have over 50 years'experience of catering for the

needs of modellers, handymen andhome craftsmen. Branches at 78a,New Oxford Street, London, and inBirmingham, Glasgow, Manchester,Leeds, Sheffield, Hull. Southamptonand Bristol. Head Office, Dereham,Norfolk.QHIPS IN BOTTLES.-TheL-7

con-structional kit that tells you how

to make them: build for pleasure orfor profits; kits 6/- ea. from HobbiesLtd., and model shops, Cooper -Craft Ltd., The Bridewell, Norwich.MODEL AIRCRAFT CASTINGS

when finished would make anice Xmas present ; easy to finishwith file and emery ; all the follow-ing 3/-, post paid : Tempest,Mustang. Spitfire, Hurricane, Welling-ton, Beaufighter; 4/-, post paid, areStirling. Super Fortress, Halifax,Mosquito ; Ashtray Bases, 3/6. Sendat once ; please state 2nd choice.Dickens' Tool & Model Shop,Thornaby-on-Tees.

MODEL RAILWAY FANS! Every-thing you could wish far in

" The Complete Model RailwayCatalogue," 140 pages, over 200illustrations, contains, Lionel, Mark-lin, Hornby, Trix, Tri-ang, X-Acto,Peco, etc. etc.: all parts and spares.Your copy, 2/6 post free from Dept.M. Taylor & .McKenna, 98. CravenPark Road, Harlesden, N.W.10.

RADIOCAN YOU SOLDER? That's all

you need to make a really goodRadio or Tape -recorder fromguaranteed Osmor components ; send5d. (stamps) to -day for free circuitsand lists. Dept. P.M.C.I., OsmorRadio Products Ltd., Borough Hill,Croydon, Surrey (Croydon 5148-9).

METAL RECTIFIERS, LT HT andEHT, connection diagram, Conden-

ser values, etc., with every rectifier; ifin doubt, let us choose suitable one.'Transformers, prim. 230/250 sec. insteps of 3v. up to 30v. 2A., 19/- (post1/6) ; many ex -Gov. types at half-price ; Sliding Resistances on ceramforniers, 33 ohms, 9W, 1/6 ea., 15/-doz. ; 680 ohms, 18W, 2/- ea., 18/-doz. Full list by return (s.a.e.)packing free, postage extra. TheRadio Services, Lr. Bullingham, Here-ford. 11

HOBBIESDOLLS HOUSE FITTINGS andPapers ; Wooden and Metal Toy,Wheels (trade supplied) ; illustratedbrochure ; s.a.e. Jasons, 135, NagsHead Road, Enfield, Middlesex.TOY CASTING MOULDS, soldiers,1

sailors, airmen, animals, etc.'Rubber Moulding Compound, 8/6 perlb.. Moulds for Plasticwork, plaques,'ornaments and Coronation souvenirs.Moulds from 3/6 each ; catalogue9d. ; s.a.e. for list. F. W. Nuthall,69, St. Marks Road, Hanwell, London,'W.7.MAKE MONEY making WoodenToys; we supply the parts allready to assemble and paint. Listfree. Elf Manufacturing Co., Dept." P," Mitton Mill, Stourport-on-Severn.GROW Valuable Living Miniature

Trees ; wonderfully decorative ;terrific new hobby ; send s.a.e, fordetails: Miniature Trees, Dept., 90,Room Two, 3, Bloomsbury Street.London, W.C.1.WATCHMAKERS

ASSORTED Pocket Watch Move-ments, 6 for 10/-; Assorted'Wristlet Watches 10 for 42/6 ;1Jewelled Wristlet Movements, 10 for

40/-. Loader Bros., 36, MilestoneRoad, Carterton, Oxford.WE CAN HELP YOU. Every mem-ber of our staff is a skilledwatchmaker and as such he under-stands your difficulties and trials.Why not send for our latest materialand tool lists gratis and post free ?Interchangeable Staffs,'Winding Stems, Buttons, Hands, com-plete Balance Assemblies, EscapeWheels, Pallets, in fact, everythingthe watchmaker requires. No inquirytoo trivial, we are here for yourbenefit. H. S. Walsh, 28, AnerleyStation Road, London, S.E.20.DEALERS AND WATCHMAKERS.I

10 Wristlet Watches, take £2the 10 ; 10 assorted IngersollsFederals, etc., 50/- the 10 ; 6medium -size Silver Pocket Watches,35/- the 6 ; 2 big Silver EnglishLevers, 25/- the 2. Merkels,Jewellers, Grey Street, Newcastle -on -Tyne.6 ENGLISH LEVER WATCH MOVE-

MENTS from gold and silvercases, my price, 15/- the -6 ; 6Geneva Watch Movements, 10/- the6 ; 3 3 -plate English Lever Move-ments from 18ct. cases. 30/- the 33 big beautiful Centre Seconds Eng-lish Lever Movements from £30 ;Watches, 30/- the 3. Merkels, theold firm, Grey Street, Newcastle -on -Tyne. Postage please.

ALL INTERCHANGEABLE WatchMaterials, Tools, etc., at rock -bottom prices ; return post. Your

requirements quoted. J. H. Young& Son, Wholesalers, 133, LondonRoad, Chippenham, Wilts.

HANDICRAFTSMMUSICAL MECHANISMS. Swiss

made, for fitting in cigaretteboxes, etc., 22/8 each. Send 6d. forcomplete list of handicraft materials.Metwood Accessories, 65, ChurchStreet, Wolverton, Bucks.

EDUCATIONALAM.I.Mech.E., B.Sc., CITY &

GUILDS, Etc. Guaranteed'postal courses for all Exams. andTechnical Divisions from Elementaryto Degree standard. Approximately95% successes. 144 -page prospectusfree on request. B.I.E.T. (Dept. 967),'17, Stratford Place, London, W.1. 4I P.R.E. TECHNICAL PUBLICA-A TIONS. 5,500 Alignment Peaksfor superheterodynes, 5/9 ; Data forconstructing TV aerial strengthmeter, 7/6 ; sample copy " The Prac-tical Radio Engineer," quarterlypublication of the Institute, 2/-11membership and examination data,1/-. Syllabus of 7 postal coursesfree and post free. Sec., I.P.R.E.,'20, Fairfield Road, London, N.8.

(Continued on next page)

(Continued from previous page)WINTERY APPROVED CANDIDATE

graded in the Technical Engin-eering and Allied Classes (adminis-trative, executive, technical) is eligiblefor membership of the Institute ofExecutive Engineers and Officers ;admission fees reasonable. Give age,industry and post held for full par-ticulars of entry to the Secretary,Executive Chambers, 241, BristolRoad, Birmingham, 5.

WOODWORKINGWOODWORKING MACHINES, Saw

Benches, complete, Tin. £4/15/-;131n. 25/101- ; Lathes, £71101- ; BowlTurning Heads, £71101- ; Combina-tion Lathes, £10/10/- ; Planers, SawSpindles, Motors, etc. 4d. stamp forillustrated booklet ; h.p. available.James Inns (Engineers), Dept. P.,Sherwood, Nottingham.

MYBLO 6IN. SAWBENCHES, riseand fall spindle, 12in. x 9in.

table, ripp and mitre fences, V -drive, £6115/-; from your tooldealers or direct from makers: P.Blood & Co., Arch Street, Rugeley,Staffs.

G.E.C. & B.T.H.GERMANIUM

CRYSTAL DIODESG.E.C. GLASS TYPE 5/.16in. x 3/16in.B.T.H. LATEST TYPE MOULDED IN

THERMO-SETTING PLASTICBoth Wire Ends for Easy Fixing.

4/6 each, postage 24d.B.T.H. SILICON CRYSTAL VALVE

3/6 each, postage 24d.Fixing Brackets 3d. extra.

Wiring instructions for a cheap, simplebut high quality Crystal Set includedwith each Diode and Crystal Valve.

COPPER INSTRUMENT WIREENAMELLED, TINNED, LITZ,

COTTON AND SILK COVERED.All gauges available.

B.A. SCREWS, NUTS, WASHERS,soldering tags, eyelets and rivets.

EBONITE AND BAKELITE PANELS,TUFNOL ROD, PAXOLIN TYPE COIL

FORMERS AND TUBES.ALL DIAMETERS.

Latest Radio Publications.SEND STAMP FOR LISTS

CRYSTAL SETINCORPORATING THE SILICON

CRYSTAL VALVEAdjustable Iron Cored Coil.

RECEPTION GUARANTEEDPolished wood cabinet, 15/-, post 1/-.A REAL CRYSTAL SET NOT A TOY

POST RADIO SUPPLIES33 Bourne Gardens, London, E.4

HIGH GRADE SURPLUSELECTRONIC COMPONENTSHEAVY DUTY WIRE WOUNDPOTENTIOMETERS. Brand new inmakers cartons. 61n. dia. 1,800 ohms.4 amp. with 3 in. skirted knob, 2216.4In. dia. 2,000 ohms .22 amp. with 3in.skirted knob. 15,-. P. & p. 1/6. HEAVYDUTY L.T. TRANSFORMERS. Prim.230 volts. Sec. tapped 4-6-11 volts, 200amps., 67.10.0 callers only. Prim. 200-240 volts. Sec. tapped 10-12 volts 16amps., 29/6. carr. 21-. Prim. 200-240volts sec. 6.3 volts 15 amp.. 1916, p. & P.1/6. PARMEKO WT. 'TRANS-FORMERS Prim. 100-250 volts sec.1.300-0-1,300 volts 250 MA. Potted TypeBrand New, 59/6. carr. 5/-. PALMERI)L.P. CHOKES 10 H. 250 MA. PottedType Brand New, 15)-. P. & P. 2/-. AllInquiries Welcome.

.1. HALLETT19, Upper Richmond Road,

London, S.W.15.

CHEMICALS &A. I tie ID APPARATUS4!

WE CAN OFFER A WIDE SELECTION OFEQUIPMENT SUITABLE FOR STUDENTS

AND BEGINNERS.Send stamp for lists to :- 14 (D/PM),SURREY ROAD. BARKING, ESSEX

MAHOGANY PLYWOOD, new, anyparoel £1 delivered, c.w.o.:

6 at 111 x 60 x +in., 14 at 12 x 27 xfin., 14 at 14 x 23 x fin., 20 at 14 x17 x +in., 4 at 23 x24 x fin., 6 at14 x 26 x fin., 10 at 91 x 30 x fin.,12 at 15 x 15 x }in., 17 at 14 x 20 x3/16in., 20 at 14 x 20 x 3/16in. Smallmixed sizes £1 1cwt., following oneside slightly glue -stained: 7 at 23 x23 x 3/16in., 10 at 20 x20 x 3/16in.,16 at 47 x 84 x 3/16in. Birch. 30at 54 x 78 x 4mm. M. Leader (1920),Gosford St., Middlesbrough.

SAWBENCHES, complete with saw,fence and guard, 12in. saw size

£10, 15in, £13, 18in. £18, 24in. £25,30in. £30 ; rise and fall spindle ;motorised or petrol driven if re-quired. Let us quote for yourrequirements. Send for price list orsend 1/- for handbook -catalogue ofsawbench design data. BeverleyProducts, Ranskill, W.20, Notts.

Amateur Radio EnthusiastsTHE INCOMPARABLE

GLOBE -KINGSINGLE VALVE S.W. RECEIVER WORLD-WIDE RANGE 11-100 METRES CRYSTAL-CLEAR NOISE -FREE RECEP-TION ELECTRICAL BAND -SPREADTUNING EXTREMELY LOW RUNNINGCOSTS

Catalogue Free. Stamp for postage.JOHNSONS (RADIO)

48. FRIAR STREET. WORCES. TCR

IMPETUS Precision PLANERSCircular safety type cutter -head Highquality tempered steel knives. Tablesmounted on machined Inclined ways.Ground table -surfaces. Fencesadjustable to 45 deg. 19.10.0.4 in. MODEL.Motorised. 218.10.0. 6 in. MODEL628.10.0. Motorise(' 644.0.0. Send forCatalogues of other Impetus' Products.JOHN P. M. S. STEEL, Dept. SO,

RINGLET. YORKS.Phone : RINGLET 3551 (4 lines).

I PORTASS 4a" x S.C. LATHECast Iron Trayand Peds in 2

lengths.

Charles Porisss& Son,

Dept. P.M.Buttermere

Works, Stuiff. 8.

BUYING NEW EQUIPMENT ?First consult our new

BUYER'SGUIDE Post Free

(returnable)

T. GARNER & SON LTD.,Hand and Machine Tool Division,6-8 Primrose Hill, BARNSLEY.

Phone : 2908.

1/0

CAN YOU BRAZE?

We are presenting free toeach purchaser of a TargetBlowpipe instructionsentitled "Secrets of Brazingand Soldering." Anyone fol-lowing these instructions canbraze and solder at the firstattempt. Send for your brazingoutfit now.TARGET FINE FLAME BLOW-PIPE (Self -Blowing) for all fineand delicate soldering and brazingjobs. 2/9 post free.TARGET FIERCE FLAMEGAS BLOWPIPE (Self -Blowing) for larger jobs.Gives fierce roaring 4 -inchflame. Guaranteed to melt

copper tube. 3/6 post free.Trade supplied.

TARGET MFG. CO. (F),Wollaston,

Wellingborough.

Britinol Soldering hillits Solve AllSoldering Problems

(As reviewed in PRACTMAL MECHANICSMay, 1953)

The " Popular " Outfit as illustrated,Britinol Spirit Blow -lamp, TelescopicSoldering Iron, Paste and Cored WireSolder, 16/3. The "Junior," as above,but without Soldering Iron, 9/6. Allitems sold separately. From ModelShops and Tool -Dealers.

BI -METALS (BRITINOL) LTD..St. Mary's Works. Bridge Road,London, N.9. S.A.E. for illustrated list.

PLYWOOD TIMBER -complete jobssupplied to specification ;veenering to order s.a.e. for quota-tion, Bromberg. Ltd. (P.M.), 129,Brick Lane, London, E.1.

MAHOGANY PLYWOOD, resinbonded, all £1 parcels ; carriage

paid ; cash with order ; satisfactionor money refunded. 7 Pc., 23in. x 23in.x 3/16in.; 50 Pc., 78in. x 21 x3/16in.' 16 Pc., 201in. x 141in. x fin.;8 Pc., 78in. x 9in. x 3/16in. ; 12 Pc.,'78in. x 6in. x 3/16in. ; 22 Pc., 171in.x 141in. x fin. ; 6 Pc., 231in. x 141in.x sin. Trade enquiries invited.Dickens. 50, Mandate Road, Thorn-aby-on-Tees.

DRAWING SERVICEPHOTOCOPYING ; 24 -hour ser-

vice ; Plans, Drawings, printedextracts on Glossy, Whatnian, Linen,etc. Ardua Photos, Castletown,I.O.M.

Make Illonep-Save MoneyCOLOUR PRINTING AT HOMEThis amazing equipment PRIN"IS any-thing, COLOURS anything, DECOR-ATES anything, and DUPLICATES.6 colours in bold design or small type.16in. x lain. BARGAIN OF THEYEAR OFFER of printer completewith all supplies. inks, etc.and FREE 10/- COURSE 47/6(7 days approval) post pd.A.P.S., SEDGEFORD, NORFOLK

WEBLEYMarvellouslyaccurate fortarget prac-

tice.No licence required topurchase for use on

enclosed premises.Write for Catalogue of AIRPISTOLS. Alit RIFLES and

Accessories.WEBLEY & SCOTT LTD.,

106. Weaman Street, Birmingham

AIR PISTOLS

Eng.

BATTERY CHARGERSReliable, easily,installed, economicalSelector switch for 2. 6 and 12 volts1 amp. In Black Crackle Steel Case withAmmeter, Mains -switch, fuses, etc.200-250 volt A.C. Guaranteed. 62/6post free, from manufacturers.THAMES VALLEY PRODUCTS(P)' (Mari," Eleanor Rd., Chalfont

St. Peter, Ducks.

WIN THAT CUP!Eliminate guesswork by tun-ing with our adjustable fanbrake. No Heat. No CoolingWater. Simple instructionsand charts. Leaflet.THE GEARMARK CO.,

Farnborough Way,Farnborough, Kent.

slantottsMa

FOUR REIGNS

L ROBINSON 6 CO. (GILLINGHAM) LTD.tondo. Chambers, GILLINGHAM. KENT. Phone non

WIRING ACCESSORIESAll goods are of a well-known manu-

facture and carry a money back guaran-tee. All cables are manufactured tothe latest British Standard Specifica-tion. C.O.D. or. C.W.O. All carriagepaid.

CABLE TRS. Flat Twin 1.044 543/-3.029 68/- ; 7.029 110/-. PVC sheathedFlat Twin 1.094 42/6 ; 3.029 62/6. Allper 100 yds. Our PVC cables are suit-able for interior or exterior use andmay even be buried in concrete. Alltypes and sizes of cables available in2.5, 50 or 100 yd. lengths. Heavy cablescut to desired length at no extra charge.Switches 1/6 ; 2 Way 2/- ; Ceiling -Roses 1011. Lampholders 10d. ; 3Pin Sw. Sockets 5A 4/6 ; 15A 6/6.Send for price list of other accessories.

HUNT & CO.,WEST STREET, EXETER.

Phone : Ereter 56687.

PHOTOGRAPHYENLARGER and Camera Bellows

supplied ; also fitted, Beers, SL'Cuthbert's Road, Derby.

MISCELLANEOUSBUILD YOUR OWN REFRIGERA-

TOR, all components availableat reasonable prices. Frigidaireflowing cold units, £5 ; small units,Kelvinator, etc.,. £4; h.p. heavyduty Motors, £3; Chrome Cabinetfittings, new, £1; money back guaran-tee ; s.a.e, for list and schematicdiagram. Wheelhouse, 1, The Grove.Isleworth, Middx. (Phone: Hounslow s7558.)

BOOKLETS " How to use ex -Gov.Lenses and Prisms," Nos. 1 and

2 price 2/6 ea, ; ex -Gov. Optical listsfree for s.a.e. H. English, RayleighRoad, Hutton, Brentwood, Essex." VORTUNES IN FORMULAS." 900

-4" pages containing 10,000 formulaeprocesses, etc., 25/- ; Americanmagazines, hobby, technical, etc.;stamp for lists. Berge, Ltd.,Hastings.

THE SCREEN COLOUR PRINTERprints absolutely anything. 55/ -

complete; send s.a.e.. for fullestdetails and samples. Dept. B., Ship-ley Sign Service, Shipley. Yorks.

ELECTRIC BLANKETS. - Makeyour own easily ; Element and

simple directions, 15/6 , state mainsvoltage. A. Stuart, 62, Hurnway,Christchurch. Hants.

P.D.5r POR10SSN29 .

TA0

Less Counter Shaft. S.S.S.C.LATHEfee. P.M.

nudesPortass & Sou.

13.1tt nntreWorkr,

81u111 -1d. 8SfaMI9 Please

RATCHET & REVOLUTIONCOUNTERS

Ask forLeaflet No. I8/1

Speed up to6,003 r.p.m.

B.&F. CARTERCo., Ltd., Biltln5

REFILL YOUR OWNKOLOID REFILL KIT

FOST FREE 3/6 PER OUTFITCOMPLETE WITH ILLUSTRATED

INSTRUCTIONS AND TOOLContains Ink for Blue, Violet,12-1.5 Refills I Red, Green.

G, H. HOLMES(Dept. t), 67, Brunswick Paris Road,

London, N.II.

EVERYTHING ELECTRICALSingle items supplied. Send for free com-plete price lists.C.G. Lampholders, 6/9 dz. B.C. Adaptors,7/3 dz. Batten Holders. 121- dz. Angle,14/- dz. Ceiling Roses. 2 Plate 816 dz.3 Plate 1019 dz. Junction Boxes, Large13/- dz. Small 11'- dz. Switches Micro.1 way 1619 dz. 2 way 19/6 dz. SwitchesPorcelain Base, 1 way 17/6 dz. 2 way 241- dz.5 amp. 2 pin S.W. Plug", 30/- dz. lamp. 3 pin551-dz. 1/044 T.R.S Twin, 100yds. 49/-,50yds.26/-. 3/029 T.R.S. Twin. 100yds. 061-, 50yds.351, 31029 T.K.S. Twin A. Earth, 100yds. 79/-.50ydS. 421, 71029 T.R.S. Twin, 100yds.105/-, 50Yds. 54/-. 14/36 Tw. Twst. Mrn.Flex, 100yds. 34/9, 50yds. 18/6. 25Yd. 9/9.14/36 Tw. P.V.C. or Flat Twin, 100yds. 17/3.7/029 Bare Copper Earth Wire. 100yds.9/6. Mem Dix. D.P. Switch Fuse, 5 amp.4/6 each. Mem Roy. D.P. Switch Fuse.15 amp. 11/2. 30 amp. 14/-. Flee. Bells 4/6.Pushes 1/2. Buzzers 4(6 each. Lamps,40 watt and 60 watt. 11/- dz. Blocks, Sin.x i in. Hardwood. L Walnut. 4/6 dz. Insula-tion Tape, 5yds. x lin., 4)-. lOyds. 5/8 dz.Cable Clips. Small 1/9. Med. 1111. Med./Lee. 2,2 gross. Electric Fires. Best quality.lEW. 40/9. 210/ 67/6. Klee. Shaving Mir-rors. Mains. 19/9. Battery 18/3. Elec.Irons. N.P. 1416. Heat Controlled 33/8.N'ac. Cleaners, Standard Model. Yll.

HALL & WAKEMAN,5, Hayes Place, BATH.

CAN YOU PLAY THE PIANO?If you are a music lover, why has e. yo, notacquired this enjoyable .accomplishment 1 Has, the

prospect of practice I pmetice Ipractice I discouraged you ? It isunnecessary. My pupils roll growsdaily. I state it in every advertise-ment. It is your assurance of

`-than success. My class is seldom less2.000 pupils. I have taught over

87,600 AND I CAN TEA= Toti(in 12 lessons) even if you do not knowa note. Ordinary musical notation onlyneed, no freakish methods. FREE Rookand advice. Bay Beginner, Moderate,Advanced. (Block letter. please./

MR. H. BECKER/Dept. 258),

The Hall,Centurion Rd.,Brighton.Sussex


Metalfix AdhesiveMETALFIX is a new combined adhesive

and cold solder which, it is claimed,joins wood, plywood, plastic, leather and allmetals quickly, neatly and permanently. Itcan be sawn, drilled, chiselled, planed,painted and polished and is useful as a filleror for making joins that withstand heat,water or acid. It is available in two kinds:as a combined adhesive and cold solder intubes at IS. 3d. and in bottles at is. 3d. andIs. 9d., and in transparent form for invisiblerepairs to glass, china and pottery in bottlesat Is. It is obtainable at all good handicraftshops and hardware stores.

Sew-Tric Small Electric Grinders andPolishers

THESE useful machines are made inseveral types. The one illustrated is

a Sin. bench grinder and polisher with adjust-able speed control. It is powered by a t/12thh.p. motor and has a full load speed of6,00c r.p.m. The price is £5 los. Similarto this is the Sin. bench double grinder andthis model is priced at £5 16s. 8d.

Also available are a 4in. bench grinderand polisher, fitted with 4ft. flexible shaft;a 4in. bench grinder with tapping attach-ment taking up to 4 B.A. and a 4in. benchdouble grinder. Each of these three machinesis powered by a 1 /6th h.p. motor withadjustable speed control and has a full loadspeed of 5,000 r.p.m. The flexible shaftfor the first of these three costs £2 los. andthe tapping attachment is the same price.The 4in. double grinder complete is pricedat £8 15s. 4d.

Another Sew-Tric grinder available is theportable model with foot -control andflexible drive. This is powered by a uni-versal motor of /loth h.p. running at 12,000r.p.m. The flexible shaft is composed of a5 mm. inner shaft, housed in a steel woundcasing. The handpiece is machined fromsolid steel and is supplied with a chuck ofo -Sin. capacity; it can also be supplied withcollets. The price is £9 los.

Opticians, jewellers, watchmakers, dentalmechanics, toolmakers, model makers, etc.,

Setc-Tric sin. bench grinder and polisher.

Change of NameWE have been advised by Mr. S. Portass

of the Portass Lathe and MachineTool Co., Buttermere Works, Sheffield, 8,'that in future his company will be known asMessrs. Charles Portass and Son.

The " Whitticase " Combination PocketLevelTHIS instrument consists of a light metal

stock, 9in. long, with one glass level which'is fixed in a tapered bush or ring. This bush'is easily removed and adjusted by a slightpressure of the thumb from the back towards

1the face of the level. The tapered bush isused instead of a complicated arrangement 1of screws and gears for moving the level'glass to any desired degree, marked on the'face. One feature of this level is that anybroken glass can be replaced in a fewminutes at a small cost.

It is manufactured with an inverted Vbase, and thus is unique for alignment ofshafting and check falls in pipework forplumbing, heating, etc. Another advantageis that it can be read at a distance abovethe user's head. Again, for roofing work,the advantages are immediately apparent tothe practical joiner.

The level is made of a rustless metal, andhas two countersunk holes, one at each end,

The " Whitticase" combination pocket level.

will find these machines useful for grinding,polishing, sharpening, milling, carving, burr-ing, tapping, engraving and cleaning on partsmade of metal, wood, glass, plastics andstone.

Enquiries should be addressed to Sew-TricLtd., Sew-Tric House, Honeypot Lane,Stanmore, Middlesex.

in order that it may be secured to a straightedge of any length. With the level glassturned round the user has a perfect plumb -rule.

The retail price of this instrument is17s. 6d. and the sole distributor is HowardStacey, 212-213, Grand Buildings, TrafalgarSquare, London, W.C.2.

Ramsgate and District Model ClubTHE " At Home " week held at the club's

premises September 21st -26th was agreat success, bringing once again the activi-ties and amenities of the club to the noticeof the townspeople.

Tuesday and Friday evenings were allo-cated to the general public, other eveningsbeing reserved for people by invitation only.On Wednesday evening the Mayor and civic

- dignatories who attended were highlyimpressed by the club's activities. On Satur-day afternoon and evening neighbouringclubs-from as far away as Rochester and

Folkestone-paid us a visit, thus enabling usto renew many friendships and make newones. Several new senior members wereenrolled.

The general standard of models and ex-hibits entered for the cup competitions wasvery high, three cups and a shield being

won by adult contestants, and a junior cupwas won by a member of that section.

The scale model of Ramsgate Harbour,32ft.= tin., and, the " oo " railway with itsengines, rolling stock, automatic signallingand surrounding scenic effects, made en-tirely by members, created much interest.

The officers, council and members of theclub as a whole are to be congratulated.E. CHURCH, Hon. Sec., 14, St. Mildred'sAvenue, Ramsgate.

Hitchin and District Model EngineeringExhibition

THE successful exhibition of the club'smodels and loan exhibits from other

organisations was held at the Town Hall,Hitchin, from October 1st to 3rd.

A wide selection of models was on viewand consisted of live steam locos. in thelarger gauges, marine section, and generalmodels including a cathedral made ofmatchsticks. Several working layouts wereavailable, including umm. gauge, oo gauge,and o gauge. A working layout of theTalyllyn Railway was also on show. Visitorsalso had the opportunity of viewing someexcellent model aircraft. The Champion-

ship Cup was won by Mr. G. J. Clark forhis pregrouping o -gauge wagons.-O. P.WILMAN, The Arcade, Hitchin, Herts.

FLUORESCENT LIGHTING(Continued from page I 19)

the light from the tube ;s thrown entirelyon to the ceiling, the tube being hidden fromview. This is only possible where there isa window or an artificial pelmet to screen thetube. The workshop should present nodifficulties in this direction, as the surfacebrightness of a fluorescent tube is only afraction of that of a bare lamp bulb-theuniversal source of light in so many work-shops!

It should be noted that the equipmentdescribed in this article is suitable for A.C.operation only, although there is low -efficiency D.C. equipment now marketed.The advantages of 'fluorescent lighting are-not so marked on D.C., as so much poweris wasted in the ballast.

All equipment described in this articleis obtainable from Messrs. DynaliteElectrical, of Welling, Kent, and similarmaterial of other brands may be obtainedthrough most electrical dealers.

10-

-It134 NEWNES PRACTICAL MECHANICS December, 1953

QUERIES andENQUIRIES

A stamped, addressed envelopz, a sixpenny,crossed postal order, and the query coupon fromthe current issue. which appears on the inside ofback cover, must be enclosed with every lettercontaining a query. Every query and drawingwhich is sent must bear the name and address ofthe reader. Send your queries to the Editor.PRACTICAL MECHANICS, Geo. Newnes, Ltd.,Tower House, Southampton Street, Strand,London, W.C.2.

Formula for Hectograph InkPLEASE send me details of a simple

method of reproducing a limitednumber of copies of manuscript andsketches.-E. Vincent (Reading).

THE duplicating apparatus which youneed is called a " hectograph." First

prepare the pad and inks:

The PadWater ... I2 OZS.

Dextrin - I 13

Sugar ...Glycerine

2

15,,

Gelatine 15 1)

Zinc Oxide I )1

The InkMethyl violet ... 1o partsNigrosin 20 '5Glycerine 30Gum Arabic ... 5 35

Alcohol 60

Make a " pad " mixture and pour thisinto a flat-bottomed metal tray, such as a

biscuit tin lid. It will set on cooling, givinga perfectly flat smooth surface.

Now take a piece of paper, write thematter to be duplicated on this, using forthe purpose the special ink. When the inkis dry invert the paper and press down-wards on the hectograph surface. Thenstrip off from the surface. The ink impres-sion will be left on the gelatine surface.Finally, take a clean sheet of paper, pressit down on the hectograph surface and thenremove it. It will have duplicated on itthe original written matter. Up to 5o copiescan be obtained in this manner.

The hectograph and ink formulas givenabove are not the only possible ones. Thereare many others that may be used. Youwill find particulars of these in any volumeof recipes and formula; which you will, nodoubt, be able to refer to in your localreference library.

Fluid in Heated Vapour Type RadiatorsWHAT is the name of the gas or spirit

used in electrically -heated vapourtype radiators, how inflammable is it,and what is the pressure allowed in thistype of heating unit?-George Beaumontand Sons (Fenay Bridge), Ltd.

wE presume that you refer to liquid -filledelectrically -heated radiators. These

may give approximately 8o per cent of theirheat by convection and the rest by radiation.They may be filled with water or oil. Theseradiators are not particularly suited to thermo-static control, especially the water -filled ones,because the high specific heat of the liquidresults in the temperature of the radiator risingcomparatively slowly when switched on. The

radiator will, however, continue to give offheat for some time after being switched offand thus provide a certain amount of heatingduring brief interruptions of the supply. Theradiators are suitable for continuous heatingrather than for short period heating. Thewater -filled type may need topping up fromtime to time and are susceptible to damagefrom freezing of the water if not warmly housedin winter.

The temperature of an oil -filled radiatorrises more rapidly than the water -filled type.The oil should have a low viscosity and a highflash point. Whilst there may be a very slightrisk of fire from a defect in an oil -filledradiator, this risk can be considered to bealmost negligible in a well -designed radiator.The allowable pressure in such a unit will, ofcourse, depend on the construction of the unit.In general it will be rather low.

Charging Lorry Type BatteriesT WISH to charge z2 -volt lorry type1 batteries using a motor -generatorset with a D.C. output of 250 volts at17 amperes. Please let me have a suitable

Readers are asked to note that we havediscontinued our electrical query service.Replies that appear in these pages fromtime to time are old ones and are pub-lished as being of general interest. Willreaders requiring information on othersubjects please be as brief as possible

with their enquiries.

charging circuit and explain how tocalculate for the necessary variableresistance to vary the charging current. -E. M. Smith (Bolton).TN order to charge a 12 -volt battery fully, weI advise using a charging voltage of about17 volts per battery. If you always had 12 to

THE P.M. BLUE -PRINT SERVICEI2FT. ALL -WOOD CANOE. New Series, No. I,

3s. 6d.*10 -WATT MOTOR. New Series. No. 2, 3s. 6d.*COMPRESSED -AIR MODEL AERO ENGINE.

New Series. No. 3, 5s.*

AIR RESERVOIR FOR COMPRESSED -AIRAERO ENGINE. New Series. No. 3a, Is.

"SPORTS" PEDAL CAR. New Series. No, 4, 5s.'F. J. CAMM'S FLASH STEAM PLANT. New

Series. No. 5, Ss.*SYNCHRONOUS ELECTRIC CLOCK. New

Series. No. 6, Ss..ELECTRIC DOOR -CHIME. No. 7, 3s. 6d.*ASTRONOMICAL TELESCOPE. New Series.

No. 8 (2 sheets), Ts.*CANVAS CANOE. New Series. No. 9, -s. 6d.*

DIASCOPE. New Series. No. 10, 3s. 6d.*EPISCOPE. New Series. No. I I, 3s. 6d,"

PANTOGRAPH. New Series. No. 12, Is. 6d.*COMPRESSED -AIR PAINT SPRAYING

PLANT. New Series. No. 13, 7s. 6d.*MASTER BATTERY CLOCK.*

Blue -prints (2 sheets), 3s. 6d.Art board dial for above clock, Is.

OUTBOARD SPEEDBOAT.10s. 6d. per set of three sheets.

LIGHTWEIGHT MODEL MONOPLANE.Full-size blue -print, 3s. 6d.

P.M. TRAILER CARAVAN.Complete set, 10s. 6d."

P.M. BATTERY SLAVE CLOCK, 2s." PRACTICAL TELEVISION " RECEIVER.

(3 sheets), 10s. 6d.P.M. CABIN HIGHWING MONOPLANE.

Is.*The above blue -prints are obtainable, post free,from Messrs. George Newnes, Ltd., Tower House,

Southampton Street, Strand, W.C.2.

An * denotes constructional details are available freewith the blue -prints.

15 batteries to charge at the same time youcould connect the batteries in series to thedynamo through a switch, fuse, ammeter andbattery cut-out, with a variable resistor also inseries to control the charging current. Theohmic: value R1 of this resistor could then bemade equal to 12o,11 ohms, where I is theminimum charging current required. Alterna-tively, if the motor generator set is to be usedonly for charging the batteries and 12 to 15batteries could be charged in series at the sametime, a variable resistor could be connected inthe shunt field circuit of the dynamo to controlthe charging current. It is not possible to statethe ohmic value of field -regulating resistorrequired without knowing the field currentand having the magnetic curve of the dynamo.However, the regulating resistor should havean ohmic value rather greater than the resis-tance of the shunt field windings.

We presume, however, that it is requiredmerely to charge one battery at a time. In thiscase a variable resistor should be connected inseries with the battery, ammeter, switch, andcut-out across the dynamo. The volt dropacross the resistor will require to have anominal value of 250-12=238 volts. In orderto limit the charging current to a minimumvalue of 5 amps, the ohmic value of the resistorR2 should have a maximum value of238 volts -48 ohms approximately. The re -5 amps

sistor must be capable of carrying themaximum charging current without reaching adangerously high temperature. If it isrequired to govern the charging currentbetween 5 and 17 amps, the resistor should becapable of carrying 17 amps.

Tables supplied by makers of resistance wireshow that 12 s.w.g. nickel -chrome resistancewire will reach a temperature of more than200 deg. C. when spirals of this wire carry 17amps. This wire has a resistance of o.062

75oft. would be required.The wire could be wound in a spiral of abouttin in diameter suspended between supportscovered with asbestos or mica, in a ventilatedframe. A considerable amount of power willhave to be dissipated in heat at the resistor anda bulky resistor will result. If the maximumcharging current is so amps, half this length ofwire could be used. Loops on the wire couldbe brought out to contacts on a tapping switchto control the charging current, about half theresistor being tapped. The length of wirerequired could be reduced by using a resistorin the shunt field circuit of the dynamo toreduce its voltage if this is to be used solelyfor charging.

Dashboard Warning Light for DynamoChargingWITH reference to your articles in the

August and September issues of" P. M." on " Car Battery ChargingControl," I find no mention of a detailthat I always find puzzling. This is thered warning light on the dashboardwhich goes out when the dynamo startsto charge.-H. Cusden (London, N.W.6).

THE ignition warning light is connectedbetween the ignition coil side of the

ignition switch and the dynamo side of thecut-out contacts. The path of the currentthrough the bulb is indicated on the diagramby the heavy line, and it will be seen that,when the ignition switch is turned on andthe dynamo is at rest, there is a circuit by'which current can flow through the bulbfrom the battery by way of the dynamowindings. When the dynamo is rotated itstarts to develop a voltage which will, attick -over speed, be less than that of the'battery but of the same polarity. Conse=quently the bulb will receive the batteryvoltage, say, 6 volts, on one side, and thedynamo voltage, which might, under these.

(Continued on page 135)

4

I

December, 1953

PICTUREMARQUETRY

by

MODELER AFTPICTURE MARQUETRY, a moderndevelopment of the age-old craft ofMarquetry, is a fascinating hobby for allages and both sexes. It produces worthwhile pictures of lasting beauty in colour-ful veneer woods, ideal as home decora-tions or for the embellishment of trays,firescreens, etc.MODELCRAFT LTD. arc happy toannounce the issue of a new series ofMarquetry Kits entitled " The Romanceof Sail." The first kit in the series isdepicted in the drawing above and isentitled " Westward Ho."The kit includes : Hardboard BackingPanel, specially selected Veneers (12 types),Hot Iron Transfer, Translucent TracingSheets, Black and Yellow Carbon Paper,Garnet Paper (2 grades), full colourPicture Guide and 8 -page InstructionBooklet.Overall size inc. border, 12in. x 10in." Westward Ho " Marquetry Kit, price1614, including P.T.

Packing and Carriage 9d. extra,From all Hobby and Handicraft stores,or direct from

ITIODELCRAtivir LTD..77L, GROSVENOR RD., LONDON, S.W.1ear

All items carriage paid (U.K. only)EZEE ELECTRIC ARC WELDERCan be used for welding, brazing andsoldering from normal 6 or 12 v. battery asin a car. Complete with spare carbon rodand welding iron. Unrepectobleat 25/-.

*bp

BLOWER MOTORDual voltage. 12 or24 v. Outlet aperture1Y.in. Ideal for makingcar. heater, ventilator,etc. 27/6.

FLASHER MOTOR UNITSContaining small24 v. D.C. motorapprox. 2Dn. x

and Reduc-tion Gear Box,driving cam oper-ated contacts,made for flashinglights on aircraft. Ideal for Flashing Indicator,Illuminators,' etc. Motor and Gear Boxuseful for all types of models, 25/,MODEL MAKER'S MAINS TRANS-FORMER All purpose low voltage.Input 210/250 volts. Output 3, 4, 5, 6,8, 9, 10, 12, IS, 18, 20, 24, 30 volts. Rating2 amps. Brand new, fully guaranteed, 24/,Set of TWIST DRILLS. 9 drills I/16in.to /in. complete with plastic case andstand. Brand new, 4!6.

Send for Xmas Gift List.Cash With Order. No C.O.D.Visit Our New Showrooms.

SHERMAN'SSUPPLY COMPANY (PM3)479, HARROW ROAD, LONDON, W.10

LADbroke 1718

NEWNES PRACTICAL MECHANICS

P/RAL &ADES

METAL -PLASTICWOOD

Three Blades andAdaptor, 2/6Extra Blades,

3 Icr 1/ -

CUT /N ANY D/RECT/ONThe round blade with its 360 deg. cutting edge is revolutionary and eliminatesthe problems of sawing intricate curves and angles which would be impossiblewith ordinary hacksaw blades and at a speed three times that of any similardevice. It cuts tubing without tearing or binding. The spiral blade (withadaptors) fits any standard frame. Blade length 10 in., blade diameter .050.

Obtainable from all leading Tool Dealers.

SPIRAL SAWS LTD., TRADING ESTATE, SLOUGH, BUCKS

BE MERRY but be WISETRANSFORMERS, A.C. 200/

240 v. to 2.5 v. and 4 v. forIlluminations, 12/6. Postage 1/6.BATTERY CHARGERS, A.C.200/240 v. to 6 v. 3 A., 42/-.Postage 2/6.Ditto, 12 v. 21 A., 42/-. Postage2/6.ROTARY CONVERTERS, D.C.200/240 v. to charge 6 or 12 v. at1,', A., 50/-.Model Railway Power Units.

S.A.E. for New List.

LAWRENCE FRANKELMAIL ORDER

134, Cranley Gardens, London, N.10.'Phone CLissold 6641, or TUDor 1404.

THE

THORLITERUBBER FACED HAMMER

Will do no damageto the part struck

Faces of tough rubber fitted in die-cast aluminium head of patented con-struction. Faces readily removed for replacement when worn. Standardsize fitted with 11 in. diameter faces weighs 12 oz. complete with handle.Price 7s. 6d. Obtainable from all good tool dealers.Soft hammers of rawhide, copper, cellulose and plastic also supplied.

THOR HAMMER CO., SALOP STREET,BIRMINGHAM, 12. 'Phone : V1Ctoria 4011 (7 lines)

Plastic MarbleKARLENITE-the entirely new Karlene artificial Stone for casting Bookends,

Ashtrays, Wall -vases, Statuettes, etc. Sets rock hard with a scintillating crystallinestructure like marble or alabaster for colour, veining, texture, density and hardness.It is enormously strong, highly resistant to heat, impervious to water. Natural" veining " can be simulated in any colour. A range of pigments is available for thispurpose. Most attractive marble effect in models, plaques and statuary.

Make your own Elastomold

Flexible MouldsELASTOMOLD-high quality synthetic rubber for making flexible moulds which

faithfully reproduce the most minute details of ornamentation and surface texture.ELASTOMOLD is permanent and ideal for repetition casting of plaques, bookends,ashtrays, and art models. Moulds can be taken from any type of material includingKarlenite, wood, metal, plaster, cement, stone, glass, ivory. ELASTOMOLD hasgreat dimensional stability, but flexes easily for the release of cast without damageto fine detail or undercuts. ELASTOMOLD is simple to use and fully recoverable.

Send for full details of this new, fascinating and profitable craft.KARLENA ART STONE COMPANY LTD.

PLASTICS 2F. DIVISIONKARLENA HOUSE 270/272, OXFORD ROAD, MANCHESTER 13,

135

GALPIN'SELECTRICAL STORES

408 HIGH ST., LEWISHAM, S.E.I3.Tel.: Lee Green 0309. Nr. Lewisham Hospital.TERMS : CASH WITH ORDER. NO C.O.D.All goods sent on 7 days' approval against

cash.

EARLY CLOSING DAY THURSDAY

ELECTRIC LIGHT CHECK METERS,useful for subletting, garages, etc., all for200/250 volts A.C. mains, 5 amp load, 19/ -each ; 10 amps, 22/6 ; 20 amps, 27/- ; 25amps, 32/6 ; 40 amps, 38/6 ; 50 amps, 46/6 ;and 100 amps, 57/6 each, all carriage paid.6 or 12 VOLT RECTIFIERS at 4 ampsoutput, complete with suitable trans-former, 200/230 volts input, 45!- each,post 1/6.

METAL RECTIFIERS, suitable for 6/12/24volts at 10 amps charging with the correcttransformer, complete with TX 97/6 each,or Rectifier only 35/- each.1,000 WATT AUTO WOUND VOLT-AGE CHANGER TRANSFORMERtapped 0/110)200/230/250 volts f5/15/ -each, carriage 4/6.Ex-W.D. U.S.A. HAND GENERA-TORS, less winding handle, output 425volts at 110 mia., at 6.3 v., 21 amps, com-plete with smoothing, 30/- each, carriage 2/6.Ex-U.S.A. ROTARY CONVERTORS,12 volts D.C. input outputs, 500 volts50 mla., 275v. 100 m/a. Complete withsmoothing, 32/6 each, carriage 2/6, as new.Ex -NAVAL ROTARY CONVERTORS,110v. D.C. input, 230 volts A.C. 50 Cy,I ph 250 watts output. Weight approx.100Ibs., E12/10/-, c/forward.MAINS TRANSFORMERS (NEW),suitable for spot welding, input 200/250volts, in steps of 10 volts, output suitablytapped for a combination of either 2/4/6/8/10or 12 volts 50/70 amps, 95/. each, care 7/6.MAINS TRANSFORMERS (NEW),200/250 volts input in steps of 10 volts,output 0, 6, 12, 24 volts 6 amps, 42/6 each,post 1/6. Another, as above but 10-12amps, 55/- each, post 1/6 ; another, asabove, but 25/30 amps, 75/- each, carriage3/6 ; another, input as above, output0/18/30/36 volts 6 amps, 47/6 each, post 1/6.MAINS TRANSFORMERS (NEW),input 200/250 volts in steps of 10 volts,output 350/0/350 volts, 180 m/amps, 4volts 4 amps, 5 volts 3 amps, 6.3 volts 4amps, 45/- each, post 1/6 ; another 350/0/350 volts ISO m/amps, 6.3 volts 8 amps,0/4/5 volts 4 amps, 45/. each, post 1/6 ;

another 500/0/500 volts 150 amps, 4 volts4 amps C.T., 6.3 volts 4 amps, C.T., 5 volts3 amps, 47/6 each, post 1/6 ; another 425/0/425 volts 160 m/amps, 6.3 volts 4 amps,C.T. twice 5 volts 3 amps, 47/6 each,post 1/6.TRANSFORMERS SPECIALLY MADETO ORDER, delivery 72 hours from date oforder. Please let us quote you.MAINS TRANSFORMERS, 200/250 voltsinput, output a combination of 6, 12, 18, 24,30 and 36 volts at 6 amps, 45/- each,post 1/6.METERS, Moving Coil, 0 to 14 amps, 18/6each. Ditto, Moving Iron, suitable for A.C.0 to 30 amps, 25/- each. Another movingcoil, 100 to 250 amps. D.C., 35/. each, all4in. scale.12/24 VOLT RECTIFIERS at 4 amps,with suitable Mains Transformer, 200/230volts input, 55/. each.MAINS TRANSFORMERS, input 180/250 volts, output 435/0/435 volts, 250 m/amps, 6.3 volts 10 amps, 6.3 volts 8 amps,6.3 volts 8 amps, 5 volts 6 amps, 65/- each.LARGE STUD TYPE DIMMER RESIS-TANCES, 10 ohms, 9/18 amps, 32 studs,35/. each.3 KILOWATTS DOUBLE -WOUNDVOLTAGE CHANGER TRANS-FORMERS, 110/230 volts or vice -versa, asnew, weight approx. 1001bs., f12/10/ -each, carriage forward.MAINS TRANSFORMERS, 200-250volts input, output 40010/400 volts, 280miamps, 6.3 v. 8 a., 2 v. 3 a., 5 v. 3 a., 4 v.2 a., 4 v. 2 a., the last two heaters insulatedat 8,000 volts, 85/- each ; another 200/230volts input, output tapped 0, 9, 18 volts at4 amps, 25/- each, post 1/-.D.C. MOTORS, 230 volts, .3 h.p., 3,000r.p.m., in good condition, f3/5). each , dittoFan Motors, 230 volts D.C., 20/- each ; 110volts D.C., 17/6 each.MAINS TRANSFORMERS, input 200/250 volts, output 45/50 volts, 70 amps,suitable for arc welding, EIS each ; another70 volts, 50 amps, fly each.

ar


circumstances, be 3 volts on the other,leaving only 3 volts available to light thebulb. It will then glow at a reduced brilliance.When the dynamo speed is raised so that itdevelops the same voltage as the battery itwill be able to fully oppose the flow of anybattery current through the bulb, which willbe extinguished. A further increase indynamo revolutions will bring in the cut-out,the contacts of which short out the bulband so prevent any current from the dynamopassing through it in the reverse direction.

The bulb itself is often of the low -voltageflash -light type and is protected againstoverload by a wire resistance wound aroundthe bulb holder. It should not be tested bysubjecting it to the full battery voltage whenremoved from its holder.

Mechanical Horse -racing GameTN an attempt to relieve the tedium1 out here, we are anxious to build amechanical horse -racing game.

We have already built one using simplya plain bar, with six pieces of asbestosstring attached to it, and towing sixhorses, mounted on wooden platforms.

The bar is rotated by means of a motor,the ropes coiling around the bar. Thedifference in the way they coil resultsin different horses reaching the winningpost first.

This arrangement does not give enoughVariation. Can you suggest an alterna-tive ?-Sgt. C. G. Armistead (M.E.A.F.to).

OBVIOUSLY the arrangement which yourequire must be simple to construct

and must ensure that the arrival of the sixhorses at the winning post must be differentlydisposed in each race. We think that theseconditions can be met by letting the cordsfrom the horses be wound, not upon a parallelroller but upon bevelled cam -shaped cheeksor, more correctly, between such cheeks,all the cams having different profiles. Thesketch shows the principle of the idea andsome possible shapes for the cams. Youmay be able to cut the cheeks from eitherplain boards or from thick plywood andglue them on your existing roller. Thebevelled edges should not be finished toosmoothly.

frregufarsurfaces

Electronic Brain"T AM making the " electronic brain "

described in the June and Julyeditions Of PRACTICAL MECHANICS. Ihave, however, run into the followingdifficulties, on which your advice wouldbe much appreciated.

(a) The steel ball switches. These is myexperience do not guarantee contactevery time. I therefore propose substitut-ing switches, preferably of the press -button variety. Where may these beacquired ?

Where may the correct Cellophane beobtained, also what power bulbs arerecommended ?-A. Wemyss (Chelsea,S.W.3).

T DOUBT whether press -button switches1 of the required pattern are available.These switches would have to be of the two -make type. Toggle switches of this typeshould be obtainable through any goodelectrical supplier. A simple press -button,as used for a bell -push, could be used inconjunction with a suitable relay. In thiscase, the relay would have to be of the three -make type, and a circuit diagram for one unitis given below.

Pushbutton

Re/ay holdcontacts

Reset switch(Normally closed)

To correspondingbulb

To terminalstrip

Relay coil

To other relaycoils

When the push-button is pressed, the relayis actuated and the contacts close. The " hold"contacts short out the push button and the relayremains closed. When the game is finished thereset switch is actuated, thus removing the" earth" from all the relays. It should benoted that the reset switch is common to all

the relays.The Cellophane or-

iginally used was pur-chased in a stationer'sshop, and it was notanticipated that therewould be any difficultyin obtaining furthersupplies. I suggest thatyou get in touch witheither The StrandElectric and Engineer-ing Co., Ltd., 29, KingStreet, London, W.C.2,or Plastics, Ltd., I1,Whitworth Street,Manchester, I.

Failing a satisfactorysupply of Cellophane,the alternative is touse several thicknessesaround the lamps to getthe requisite depthof colour. (This shouldonly be necessary withthe green Cellophane.)If several thicknessesof Cellophane are

necessary, it would be a good plan to use col-oured Cellophane or gelatine to form theletters on the glass. This method would be lesstroublesome than attempting to build up theletters out of several thicknesses of Cellophane.

The lamps used are the standard 2.5 volt0.3 amp. For best results, they should beoverrun. This cuts down the bulb life butgives a much brighter light.

Screweye

Suggested arrangement of bevelled cam -shaped cheeks for horse -racing game.

It is improbable that each individual cordwill behave in exactly the same way although,in each race, it is wound upon the same cam.We think that the races will be more realistic"than at present because the speeds of thehorses will vary owing to cords climbingthe bevels and then slipping back to smaller

/71 diameters. All the cheeks should have thesame external circumference.

December, 1953

Fireproofing ThatchT WANT to re -thatch my house with1 grass, but before doing so I should liketo know if there is a satisfactory way ofmaking the thatch fireproof.-L. A.Veary (S. Rhodesia).

ASOLUTION which Rural Industriesadvise as suitable for fireproofing straw

is put forward as being in all probabilitysuitable for treating grass. It would be aswell to test a batch after treatment beforegoing right ahead.

Make up the following :28 lb. ammonium sulphate.14 lb. ammonium carbonate lump.7 lb. borax lump.7 lb. boracic acid.

14 lb. alum lump.Dissolve this in 5o gallons water. Soak

your grass in this solution and allow to drainover tank on slats for three hours. Thisquantity will treat 500 sq. ft. of thatch.

Imperial Chemical Industries market apreparation called " Faspos " which they stateis suitable for reeds only.

InformationSought

Readers are invited to supply the requiredinformation to answer the following queries.G. C. Roberts writes : " Please advise me

how to arrange stage curtains at our VillageHall. The length of the stage is approximately22ft. and the height of curtain is 9ft. Thecurtains are in two halves, and I should liketo operate them on a drum rather thanpulling on the ropes. Operation will be byhand, and not by electricity."

J. Courtney writes from Musselburgh :" I intend to build a hand bench drill to takea in. or lin. chuck. Can you give me anyinformation as to proportions of bevel gearsand construction of drill in general also sup-pliers of gears ? "

J. Fearn asks : " Could you give me adesign for a paraffin vaporising burner, tobe used in burning weeds in a marketgarden ? I have a pressure tank with pump,and would like a broad flat flame in theburner. I am a skilled engineer and have thefacilities for making necessary parts."

J. P. Owen writes : " Please give medetails of how to build photo -electric cellequipment to release the shutter of mycamera which is synchronised to electronicflash. The sketch below shows my idea.The object to be photographed interrupts thelight beam, the amplifier activates the solenoid,which trips the shutter, which in turn firesthe flash.

" The equipment I wish to build is fromlight source to solenoid in the diagram."

Flash unitSolenoid

Light source

Camera

Light beamPhoto-

electric rell

Amplifier

NEWNES PRACTICAL MECHANICS - WorldRadioHistory.Com...December, 1953 NEWNES PRACTICAL MECHANICS 103...

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