T H E

JOUI~NAL OF

F R A N K L I N I N S T I T U T E

OF TIIE

5tare of ~ruu~t~ctnia

A ~ D

A M E R I C A N R E P E R T O R Y .

O C T O B E R ~ 1 8 4 t : ,

CIVIL ENGINEERING.

,Shine account of Leveling hzstruments, wilh a description of one of an imflrovedform. Bff TIto.~as STeVenSOn, C.E., Edinburgh. +

The improred spirit level about to be described, was made for me i~t 18t0, by Mr. Adie, and afteruTards described in a letter to the ln- stim~ion of Civil Engineers.?

Since then I have had two levels, of the common construetioii, altered to the new form. On a late occasion, these instruments were exhibited to the Royal Scottish Society of Arts ; and~ as no drawings had been laid betbre the public, that Society requested me to prepare a description \vith diagrams, that these might be published in their Transactions. in aceor:lanee with their request, theretbre, I have drawn up the present description; and have also consulted many early writers, to ascertain, as well as 1 could, the history of one of the most important of geodetical and engineering instruments.

There unfbrtunately exists a great deal of conflicting evidence regarding the true inventors of the different parts of the spirit-level. Indeed, there are t~ardly two authorities who agree upon the subject.

The great I luygens appears to have been the first to app@ l/~e leleseope lo a level of his, which was constructed on the pritmiple , / the plummet. This is noticed in the life prefixed to his works,l: i1~

* Exhibiled and verbally described to the Royal Scottish Society of Arts~ on lhe ~2d January, ;,~44; and this written description requested.

]'Engihe~r ~nd Architect's Journal, vol. v. Christ. ttugonii Op. Var. I,ugd. Batav. 1724.

VoL VIII, 3ao Sl~Rir, s ~ N o . 4 .~0e 'ros~a , 1844, 19

218 Civi l Engineering.

the following terms: - -" I b i " (Lmet im) " v i x i t ab anne 1666 ad a n n u m 1681. Durante hoc tempore pulcherr ima snbtitissimaque multa in mathematicis detexit var iaque e x iis operibus conseripsit queo mine in unum corpus collecta quid in vari is Matheseos partibus pr~stiterit sub oeulis ponunt. Printer ipsius j a m memora ta invents praJelara inter alia duo insigni usu eminent . Zi8ellam telescoSo m~tnita~z its construxit ut ipsi prm eeteris tides haberi poss i t / ' &e.

The baser of having first appl ied {he air-bubble to the determine. tion of horizontality, seems to be title to that universal genius l)r. Hooke. From all that I can gather, it appears that his iavcntion must have been made subsequent to 25tit March, 1674~ and prior to the year 1675, as~ in his " A t t e m p t to prove the 5,lotion, of the Earth by 0bserrations~" of date 25 th March, 1674; he describes a now method of alilling gee p lummcl , by immersion in water. \Virile il~ his animadversions,* published also in l(iT,~I., after ihily descril)i;~g his invention of the air-bubble conf ined in a lube, he spc~'aks of its pecu- liar advantages, and great delicacy of movement , and rcmarks,-- "This can hardly be per fo rmed by the ordinary way of t)hmm~ets, without banging fl'om a vast hoigi~t, which is not practically to })c perfbrmed without almost infinite trouble, expense, and dilEeulIy,'" &e.

Hutton, in his MathematieaI Dictionary, remarks, tibet the applica- tion of tim air-bubble to the level, "is said to be due to M. ThevetJol," but with what justice I canno t say, having been unable to meet will, any refc~rence to this ins t rmnent in the writings of that author. Thevenot was born in t(~21, a n d he died in 16952.

I have been unable to discover who was the inventor of the ci~'c~e- lar level, which, I imagined, h~d been of recent date; but Switzer, at page 91, of his Treatise on ~Zater-Works, which was published in 173% remarks, that the c i rcular leveI was then employed in the eon- struetion cf the surveying ins t rument called a plane-table.

According to Sir John Hersehet~ the c,'osa-/zc, g,5 which gives so much accuracy to all astronomieal~ as well as leveling, instruments. was the invention of gasem,3n % a young Englishman, who used it in 164o. He was killed, at the age of 28~ at the battle of 5'~arsto~ Moor.

5,~I. Le igion? appears to have been the first to co~}~oin lee telescqpe q f []~.ygens with the ai~'-auhhZe of Dr. Hooke ; and this must have been subsequent to the year 1 (384, as such an instrument is not shown in De ta Hire's edition of P i ea rd ' s Treatise on Leveling.$

But il; was not till Siscson's improvements that the level could be considered as iu any way an accurate, or philosophic, instrument.

A~i,~! dversions on the first part of the Machine cmlestis of the Hen., learned, and de- servedly f~,na~.,.s Astmn. aohanr~es Hevelius, Oon~ul of Dan~zick, together with an explication of some -~.~r~',mo~nts made by Rob. IIooke, Prof. Geom. in Gresh. ColI., and F.R.S. Lend. 1674 , p. 6~, ~ et ~eq.

l"['zai% ~c ta Conati:~aetion et de~ Priacipanx usages des Instrumens de Mathematique. P a r N. Im Bion, tngcnieur du I{oi pour les Instrumens de Math. Near. Edit. a la Haye, 1723.

# Traitd da NLeilement Par ~L Picard, mis on lumi~re par lea soins de M. Do la Hire, l~mo. A Paris, 168~t.

On an [mt~roved Leveling Instrument. 219

All that were made previous to this t ime were coarse instruments, adjusted by a ball and socket, and, in other respects, resembling the common perambulatory survey.level, which, from the nature of the construction, call be leveled in only one direction, and cannot be reversed, or moved, even ill tile slightest degree, without requiring re-adj.stme~m Sissou may, therefore, be considered as the inventor of tile instrument in common use. The main feature in his improve- ments wa:s the introduction of tile four screws called the parallelplate scre*vs, (D, in the diagram.) I have been unable to find out the date of Sisson', in~provement ; and, indeed, the only notice I can find of him is *!~; ibl!owing itl Switzer's System of ~,'Vater-Works:---The invetltiol~," alluding to the instrument with parallel plate-se~rews, "as I take. it, (for I am not as yet well a(:quai:~ted with that gentleman,) of William Sisson, at the corne, r ofBeaufbrt Bttildings, in tile Strand. ' 'a

Since the lime of Sisson, the celebrated Ramsden introduced a tan- o.ent screw and clamp, lbr moviug the instrunmnt with accuracy ihrougI~ small distances ill an arimuthal direction. Messrs. Troughton ',,.rid Simms also made several improvements in the arrangement of Ibe various parts of tim i' ,strument; and Mr. Gravatt, has, of ]ate years, added a eross-[ml~bh', fbr facilitating lhe rough-selling of tile in~_qrumet~t--or that aclju.~tment which is made with the legs of tile vripod; and an enlargement of tile diameter of the object-glass, so as, l~y the admission of a greater nulnber of rays of light, to allow of the ~qescope being shortened, without impairing its optical powers.

Having thus endeavored to describe the successive changes which ,qm level has tmdergone, 1 shall now proceed to notice the nature of the prescott improvements.

3'he first of these is the substitution of a circular, or, to speak more correctly, a sTJhevical level, G, sluggish in its motions, instead of the small cross-level, which was introduced by Mr. Oravatt. The advan- tage of the circular level over the common form, is its peculiarity in at once showing the deviation of the instrument from horizontalfty in both directions, instead of only one.

Betbre describing the next improvement, it may be proper to state, that tile clumsiness of the common level consists in its being at all dependent on the setting of the legs. This arises from the cireum- :stance of tile bali and socket motion, K, being eontrolled in its action by the parallel plate screws of Sisson, D, the consequence of which is, that, in using tile common level, care must be taken to set the ip.strument very nearly level by the e~ae, so as to be within the range of' the parallel plate screws, I), otherwise it is impossible to adjust the instrmnent. And, although to the practical man, the trouble attend- ing this may be comparatively small, still he will admit that it is o n e of the most irksome paris of the whole operation of leveling ; to say nothing of the time that is lost in adjusting the instrument afterwards, with the parallel plate screws. What appeared to be wanting was a motion for the preliminary, or rough.setting, intermediate in nicety between those of the parallel plate screws, and of the legs. In order

" An Universal System of Water and Water-Works; by Stephen Switzer, ~ vols. 4to. Lend. 1734.

~ 0 G i v l l ~nginee~'ing.

to gain this end, a bah a n d socket motion~ F, having a elamp, N, is introdueed in addition to the ball and socket, K, whose action is lim- ited by Sisson's paralM plate screws, D, so lhat ~ improved level ha~ two ball and soeleet ~nover~zenls.

~;£ - =_2.~.-

fJ

A

7 ¸

A B, is the telescope; (I C, the compass box; M, the screw ~br ad- justing the focus; H H, the tubular spirit-level; G, the spherical, or circular, level; D D D, the parallel plate screwsof Sisson; K, the old ball and socket motion; F , fl~e new ball and socket motion; N, clamp- ing screw for socket motion.

With the instrumm~t thus improved, the observer is made qtfite independent of the level o f the ground where he sets the legs of his instrument, and may place them without regard to the inclination of ~he telescope to the horizon. Looking first to the circular level, G, and releasing the clamp, N, of the bait and socket, F, he, with one hand, moves the head of the instrument tilt the bubble is in the centre of the circle, a~t operation which is done almost instantaneously?"

* In the annexed plan the instrnment i~ shown off lhc level, so that neither the air-bubbl~ of the circular level, G, is in the centre of the circle; nor does the air.bubble in th~ tube, H H, eorte~poad, with the fiIe-mark~ made on the gIass.

Mine~'al and 31elallie ,~latisties. 221

The socket screw, N, is then clamped, and the telescope bubble H H, is brought to the al)solute level by a slight touch of the parallel plate screws, D. In this way the l e g s o f t h e tripod never need to be moved after lhe instrument has been placed on the ground, and the paralle[ plate screws have ahtmst nothit~g I,.) do--advantages which all who are accustomed to leveling \viii fully appreciate.

In leveling over ~:~out~taiuous districts, it very often happens that it is desirable to select a station xvhere the ground is so rugged and precipitous as to reu~ler it di[ticult, if not impossible, to find three poirlts tbv the extremities of the legs of the instrument to rest on, which shall be on such levels as to bring the telescope within the range of the parallei plate screws; hu! wide,'ever the inslr~.~.ment can. be made io s tand w i /h sc4/'ety, the Dubble o f the improved level can be adjusted, a~zd a@usled i~z exaelli~/ the same time, a~ad wi th ex- aellff lhe setme ease~ (zs i f lhe insh .ument we~,e placed on level ground/.

Another advantage of these improvements is the removal of a great practical diiSeully which is often experimmed on sloping ground. The instrument being set and properly adjusted, the observer, on looking tin'ough the telescope, may discover tliat he is not within the range of the leveling staff ; in other words, he has chosen a station too high, or too low, to admit of his.seeing any part of the staff within the field of the object-glass. The only reme.dy for this is to choose a new station where the instrument must be again set up and levelled, at a great expense of time and trouble. In order to remedy this, it was my in~emion at our time to have fixed on the telescope a French level, on the principle of the plnmmet, in order speedity to discover, before making the adjustments, whether the intended station were within the range of the staff, or not. But the instrument can be roughly set with so much ciuiekness , by means of the additional ball and socket, that tim French plummet may be considered as being now scarcely neeessaryo

In my letter to the Secretary of the Institution of Civil Engineers, I pointed out the advantages which would result to the surveyor, were the theodolite provided with a second bail and socket motion; but no opportunity of trying this has as yet occurred.

Edinburgh New Philos. Journ.

21~ine~'al and 2tfetallie ,YtatistiCs.

By the returns to five several orders made by the t touse of Com- mons, which were obtained by the exertions and perseverence of'.Sir .1. J. Guest, Sir C. Lemon, and Mr~ Evans, (M. P. for North Derby- shire,) "~ve are enabled to lay betbre our readers a most correct account of the various exports and imports of iron and iron ore, hardware, cutlery, &c., copper ore, copper, tin, zinc, lead ore, and lead, ['or tt,c year ending January 5, 1841.

Commencing "~vilh iron, it appears there was imported in the year, iron ore 131 tons, chromate of irou 139a tons, pig-iron ~4{I tons, un-

19.