The Difference of Longitude between the Royal Observatories of Greenwich and Paris, Determined by...

The Difference of Longitude between the Royal Observatories of Greenwich and Paris,Determined by the Observations of the Transits of Mercury over the Sun in the Years 1723,1736, 1743, and 1753: By James Short, M. A. F. R. S.Author(s): James ShortSource: Philosophical Transactions (1683-1775), Vol. 53 (1763), pp. 158-169Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/105718 .

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[ I58 ]

and alfo to place the lealrer exadcly in the center. By whicll means there has been no alteration required fince they were firt} fixed > and the engine continues -to Swork as evens and true as it is poElble.

I have applied wheels for reducing fridion to fome other - engines with great adsrantage} which l ffiall take the liberty of laying befbre the Royal Society fome other time; and fear I have trefipaXed too much. On their patience already by this long detail

XXIX lte Diffierence of Long*tude betweeg the Royal Qbpervorees jf GreenXwich and Paris, Mes frinecG b3w be ObJEatxas f the 74r6gnss af Mzrcury Eover the Sun S the ErS I 7 23 T736, I743, and I753 . By

JamesShort) M*X F.R.SX .

, * .

ReadJune* T T will, ne doubta appear surprlzlnga 763- 1 that I Ihould attempt to determine the

diSrence of }ongitude between two of the molR ce- lebrated obServatories in Burope; and in which fome of the gr&ateR afl:ronomersf that ever lived, haveX for above eighty years, been conRantly obServing the .motions of the heavenly bodies: yet it is moR certainX that to this day, we are ignorant of the faid difference of longitude: the Englilh aRronomers reckoning it to be = 9' 20J', and the French Set- ting it down at 9t lotta whicha they tell us, was

found

[ I58 ]

and alfo to place the lealrer exadcly in the center. By whicll means there has been no alteration required fince they were firt} fixed > and the engine continues -to Swork as evens and true as it is poElble.

I have applied wheels for reducing fridion to fome other - engines with great adsrantage} which l ffiall take the liberty of laying befbre the Royal Society fome other time; and fear I have trefipaXed too much. On their patience already by this long detail

XXIX lte Diffierence of Long*tude betweeg the Royal Qbpervorees jf GreenXwich and Paris, Mes frinecG b3w be ObJEatxas f the 74r6gnss af Mzrcury Eover the Sun S the ErS I 7 23 T736, I743, and I753 . By

JamesShort) M*X F.R.SX .

, * .

ReadJune* T T will, ne doubta appear surprlzlnga 763- 1 that I Ihould attempt to determine the

diSrence of }ongitude between two of the molR ce- lebrated obServatories in Burope; and in which fome of the gr&ateR afl:ronomersf that ever lived, haveX for above eighty years, been conRantly obServing the .motions of the heavenly bodies: yet it is moR certainX that to this day, we are ignorant of the faid difference of longitude: the Englilh aRronomers reckoning it to be = 9' 20J', and the French Set- ting it down at 9t lotta whicha they tell us, was

found



[ 159 ] found by M. Cafl;ni, by obSeraration-s of the eclipfes of Jupiter's firA fatellite tnade by himt whilll in Lon don 1n the year I698: we are no where told, that I know of, by what obServations the Englilh aIlro- nomers have fixed this difference at 9' 20tt.

In the Memoirs of the Royal Academy of Sciences at Paris, for the year I734, there is an account given of thirty-three correfponding obServations of the eclipfes of the firft fatellite of Jupiter, made at Greenwich and Paris, from: the year 1677, to the year 170I : The mean of thefe thirty-three obSer- vations gives the difference of longitude between Pa- tis and Greenwich 4- 9' 29".

I had lately the horsor to deliver to thts Saciety) a paper concerning the parallax of the Sun, deterxnin- ed by the obServations of the late tranfist of Venus: In that paper I tool notice that obServations of the tranIlts of Venus and Mercury over the Sun, have al- ways been looked upon by aRronomers, as very proper for determining the differences of longitudes between the places where fucll obServations have been made. I have calculated, and it may be dpmorlIlrat- ed, that? if we compare the obSerl7ations of the late tranfit of Venus made at Greenwich) and by M. de la Lande at Paris, and fuppofe that the difference of longitude between theSe two places is 9'25', it will follow that the Sun and Venus are at an infinite diIlance, which ts abfurd. Againy if we fuppoSe the difference to be greater) it will follow, that the Su11 and Venus are more than infinitely diItant, vsrhich is: likewiSe abfurd. We are therefore certain, if thefe obIervations are to be depended on, that the diier- ence of longitude between Greenwich and Paris is

lel;



[ I6O ] ZeSs than 9t 2St. If we compare the obServations made at Savile-houSe with the fame obServation by M. de la Lande at Paris, and reafon. in the fame manner, we ihall find that the di*erence of longt- tude between Gr@ensvich and Parisx muR be lefs than 9' 33". Thus far, therefore, a limit, one way, is fixed for the difference of longitude between thefv two places.

The late tranfit of Venus was the only one which had ever been obSerared at Greenwich and Paris, and by -comparirlg the obiervation at Ckreenwich, with that made by M. de la lLande at Paris, the difference of longitude comes out-9' 8", and if we compare ehe obfervations at Savile-houSe (30" of time weI} of Greenwich) with that of M. de la Lande $ the faid difference of longitude comes out-9' -I6ot. Since. therefore, we ha-ve only this one tranf1t of Venus, by which we can determine this diSerence of longitude, we emuR have recourfe to Fe tranfits of Mer- cury, of which there have been four flnce ie year I723, obServed at London, at Greenwich and at

* bI. de la Lande faw the internal contaA of Ye- h t tJ

nus 77vith the Surl's limb - - at 8 28 25

PereClouet - 2 -- - -- at 8 s8 z.6

M. Meffier --- " --- at 8 28 27 M. Ferner -at 8 28 29

M. de la Caille - - -at 8 28 37;

M. Maraldi a - -- - at 8 z8 4t

Since, therefore? the!obServations of mefl*leurs Maraldi and de is Caille differ fo much from the obfervations of the firk four gentlemen (who agree rery-nearly together) it is plain that they ought to be rejedred; and indeed M. de la Caille faysX in a letter to Dr. Bevis, thawt t}le telefcope he obferved with was a bad one, and confequently his obfervation not to be depended on: 1M. de la Lande favs the fame in a letter to Mn WIatkelyne, read at e Royal Society. ,

Parss.



[ I61 ] Paris. I harre, therefore, extradl;ed from the Phile fophical TranSadrions, and e Memoirs Qf the Roy- a1 Academy at Paris, the feareral obServations of the four tran&ts of Mercury over the Sun in the years I723, 1736} I743a and I733-

The obServatlons in the year I723, wew mie by Dr, Halley at Greenmrich, by Dr Bradley at Wan tled, and by Mr. George Graham at London, by mefl seurs Cani, Maraldi, and De L'iRe at Paris ThoSe in the year 1736, were nn.de by Dr. Bevis at Greenwichs and by meEseurs Cailni and Maraldi at Paris Thofe in the year I743, were made by mef fieurs Gsni? raldi, Le Monnier and de la Caille -at Paris, and by Dr. Bevts -and mySelf at Mr Gra_ ham's houSe ta Fleet-Ilteet, ndons Thole in the year I753 were made by meflbleurs Caflins, Bouguer, de L'ine, Merville, Ibours le Gentilg and de la lLande at Paris, and by Dr Bearis and myfelf in SuF

_

ry-itreet, Lonc on. By mens of thefe obServations, I haare got no leSs

than 63 determinations of the difference of longitude betweexl the royal obSertatories of Greenwich and Paris, and having correded iem by parallaxs they are as follows.

vOL. LIIt, t723 BZ



723. By the internal contadc at ingrefs obServed by Dr

Halley. M ^e#Xnt 8 /8

-9 Z3 9 4

_9 14 -9 23

asalls<^ _ _

de L'ille - de L'ine -, -L _

Maraldi- _ _ Dr. Bradley.

de L'iSle e Zn " n-

CaMlni 1-- | - Maraldi _ - de L'ille

Mr. Graham.

de Lsifle -- - _ :

CaElIli - _"111 - . Maraldi -- ---- --:

de L'iI1e - 11 1 . _ ^ :

I2

I2 2t I

I2

9 9 9

9

=8 s6 -9 S -9 5 = - 8 36

,

2lI IO 22|9: I2

t736. By the exterml contad at egrefs obServed 6y Drv

BeViS. M. Maraldi . - _ , 11- = 9 37

CaElni, jun. -1 l",l -- = 9 4+- Cafl mi, fie%. _ _ = g I 4

l l ' / /}

3128 359 3r

0743* By

[ I62 ]



By the internal contadc at cgrefs obServed by Dr Bevis.

M. delaCaille _ = 9 4, 5 Maraldi - - , _ g I8, 5 Le Morlnier .- - n .-8 53, 5 Cafl lnl, Sen.- "- -- -; 9 33, 5 Cafllnl, iun. " - _-9 s7, 5

1 | / JJ 5146 17, 519 t5, S

- 1743* By the external contadc at egrefs obServed by DrW Bevis.

M. de la Caille - . - -g I6, &- Maraldir ,- . - -9 36 S LeMonxlier_- = 9 23 S Ca«lNi, fien. - - - --- _ 9 20a 5 Cafl lni, jun. _ - -9 42, 5

_ / If

5 47 I 9, 5 9 27s 9

t743 By the internal conta?c at egreSs obServed by my

felf. , .,

M. de la Caille .-8 57, 5

Maraldi r 9 I T, S LeMonnier . = 8 46, 5 Caflini, Sen. ! - 9 z6, 5 Cafl lni, jun. , | , - -9 20, 5

r / -// 9 sXs 2743 By

sl 45 42, sl z 2

w

" I63 ]



[ 164]

By the external contaec at egrefs obServed by my

M.delaCallle _- _ 9 xg, 5 Maraldi___ 9 38 5- - Le Monnier "- _ _ 9 s5, 5 Cailns, fen. "- "-- 9 22, 5 -Cafl:ln-i, jun. -0- -_ 9 44, 5

1_1 /

5147 29 319 29? X I 753.

By the internal contadc at egrefs obSerared by Drv Bevis ? ,, ,./

M. CaElni -. 9 25, 5

Bouguer- -- _ -9 6, 5 deLine_- --- = 9 S S Merville 1llW -9 I, 5 Libour - ---Z -' -5v' °x S

Le Gentil -- -- _ 9 9, 5

- de la Lande a - - - _- 9 3, 5 I --- I, ##

7163 52, 5f9 7, 5 0753

By the esternal contaft at egrdi oSfed 6y 1= Bevis. . F 8

M. Caffini * - -9 z6, S

Bouguer I\ , _-- 8 57, 5 de Line - - _-9 7, 5

Nlerville = 9 9 S

Libour - -, _. - 9 3Q. S Le GSentil - ,. : " r | _ 9 26s S delaImde ___925Z5-

I_1, ,, 7 65 I 3, SIQ 19



By the internal contadc at egrefs obServed by my

M CaR*lni _ = g I§ S

Bouguer - w-= 8 59,> 5 xleL-lile_" " " 8 t8 -r Merville- -1- ,- - = 8 54, 5 Libour__ 8 53 S Le Gentil - - _-9 2, S de la Lande ,- 2 " "|1 _ 8 56, 5

_ J' ), 7 :63 3, s 9 o>

By the aternal ¢ontads at egreii * relf.

kr rs s*: .. _ _ .^. _a^^44^ * , , I y

Bouguer_ = 8 de LSine _- Merville _ _-9 Libour- - i - 1 _ 9 Le Gentit-_ = 9 de Ja Lande i -|- | -i . o 9

7 64+

*;erfet- br my; ,

2x, g S3 5

O ,S l5X 5 26, s

:2' 5 sI, 5

__s

. X, >.

4S*-519 t5X-

Tlie mean of theabove IO means is - = 9 Iz, 7 lZhe mean of thc above 63+ r¢fults oflt

ffie diR?erence of longitade between t _ 9 IS Grwich; and Patis is 41 | | _-J

The



[166 ] The mean of 43 refults which differl , z

not more than 15'' from the mean t-9 Ih of the whole is_ - - " - J

The nlean of I9 refillts which differ] lefs than 15t', and more than 8Xl8* 9 I4, 2 from the mean of the whole, is - .J

Themean of 24 refults which differ] lefs than 8tt from tke mean of > the >-9 I7, 5 whole is > . - _ - -3

The mean of fhe abofW J mearws iS t' ' 9 I 5> 8

And even the mean of thofe 20 refults which dif fer more tban I5" from the mean of the whole, and which are rejedled, giares the faid difference -9t I2tot, which differing only 3" from the 43 refillts, is a ;pro of:-the great sccuracy ln the deter_ mination of the differences of longitudes by obSersia- tions of the tranfit o£ Mercury over the Sun.

Let us now exarbine the limit of the errors in thefe IO Several fe¢: of deterninat-ionsj -and we lllall find that the limit of e trror-s iR- ie year

is = 27 by the^tere*lvcontadc;atjingrefs I736 IS = 3o Sy the external contaft a t egrefs. I743 iS-4e * by the internal contadc ategrefs.

is _ 26 by the external contadt at egrefs. I753 iS _ 25 by the internal contad at egreSs. s753 is _ 33 by the external contaft at egrefs.

* If we reJed the obServations of M.' le Mvnnier, in wbich there feems to be fome mikake, becauSe it differs confiderably from the refi, the limit of the error vYill be _ 9t agreeing nearly with the other limXts.

From



[ I67 ]

From hence we may fafely conclude that the difference of longitude between any two places may be determined by- one fingle obServation of the contaft of Mercury with tl.we Sun's limb, made at each place, fo that the error in the determination will not exceed 30" of time from the truth: whereas in the above 33 obirvations of the eclipfes of the firll fiatellite of Juwpiter we find the limit between the errors to a- mwount to 3' 44X' of time. If we take a mean of the faid obServations of the firlt fatellite, the difference of longitude between Greenwich and Paris is-9' 29t', and if we rejeEt thoSe which differ the moll from the refi, the mean of the remaining 25 obServations gives the faid differencB-9' 40") and the mean of thofe 8 obServations, which are rejedced, gives the faid difference-8' 53", both which laR determinations can be proved to be very fir from the truth by the obScr- vations of the late tranfit of Venus; for by the faid obServations of Venus ie appears that the difference of longitude between Greenwich and Paris cannot exceed 9/ 331!a as I faid before; and if the raid difference is _ 8' 53't, then the parallax of the Sun, lzy the Savile-houSe obServation compared with that of M. de la Lande at Par}s, wtould amount to zc>" which we are fure it cannot be.

Upon the whole therefore we may cnnclude, that the difference of longitude between the royal obSer vatories of GreenwiEh and Paris (as determined by 63 obServations of the contad of Mercury with the

SunSs limb made at each place) is g' I6/t. This de-

termination would have been perhaps more decifive, if I could have had recourfe to the books containing the obfiervations of the late aRronomer royal, Dr.

Bradleyt



E t68 ] Bradley. ObSerstations ! made by one of the greateR aRronomers, and by ehe belE and moll accurate ob- ferver, afl lfted by the beR and moR accurate infiru- ments, which are in any obServatory: But alas! the public are hitherto deprived of the uSe of theSe moR excellent obServations*.

In a former paper which I had the honor to give into the Royal Society, concerning the parallax of ehe Sun, I therein aiEumed the diffierence of longitude between G>reenwich and Paris to be-gt IOtt; and as the determinat}on of this diffierence is now more certain by the tranfits of Mercury above men- tioned, being found = g' I6"; and as this difference of longitude will make fome fmall difference in the refult of the faid parallax from the obServations made at all thofe places +, which are to the eaR of Green- wich, where the late tranGt of Venus was obServed: I have therefore computed them again, and they are as in the following fynoptic table.

* On Thurfday Sollowing, being the 9th of June, a motson was mades at the meeting of the Royal Societyy by the Rer Nevil MaRelynes F. R. S. and unanimoully agreed to, recom- mending it to their Council, as vifitors of the Royal Ob&raratorys to take proper meafures for obtaining and fecuring the aPtrono- mical obfervations, that have been made there in times paR, for the benefit of the publick: It was alfo agreed on to publifl] them, when obtained, at -the expence of the Society; and for the fu- ture, to publilh the obfervations made at the Royal Obferratory annually, in thc Philofophical Tranfaftions.

+ BecauSe the-longitudes of all thofe places were taken from the Contoiiancc des S-emts, and the Stoedi./b sSbs, in which their difEerences of longitude from Paris are marked down,

The



[ 169 ] The time of the internal contad of Venus witll

the Suns litnb obServed at the Cape of Good Hope compared with that at Sun's Parallax.

/

Greenwich _-8, 42 ---^ X

Shirburn-CaRle - 8, x5 2

57i -- 3 69-+ 54, 1 1 3 54 -- 6 74 7 33-8 60-9 59-io _ 1t

. ,. .. .

J J w s

yX 1. _ WtS .^t

68 " tnl I3 09 " 1.1_114; I4

43 - IJ XS

_ n _ s

8

_ ,

4 - 8 , W

-8, _ {, --8 - .,

-s- --_ , -8 _ X

-8 _t ,

1- * r

-8 _ ,

Q _ oa

-8 _ ,

Savile-HouSe _ Lo

es eeard _ - Paris;---- - * Bologna _ ^ --

Rome " "" _

Drontheim Upfal--- - | - -" - - - Stockolm _

EIernofand -" -a

Caimar _ - - | Abo- -- - - - - - - Tornea - --- - _ Cajaneburg - --

By the mean of theSe x5 refults theSun's z parallax on the day of the tra;fit ; 3 _ 8 54

And if we rejeEtzthe 2d, Itth, 12th,) and x4thX which differ the moft from I thereIl, the mean of the remaining t-8} 56 eleven gives the Sun's parallax _J

Therefore the mean horizontal parallax

of the Sun is _ _} = 8, 69

XXX. Ax VOL. LIII. A a



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