An Account of Observations Made on the Mountain Schehallien for Finding Its Attraction. By the Rev. Nevil Maskelyne, B. D. F. R. S. and Astronomer Royal

Nevil Maskelyne
1775 Philosophical Transactions  
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A committee was in confequence appointed, of which number I was ones to confider of a proper hill whereon to try the experiment, and to prepare everyFthmg neceSary for car rying the deIlgn into execution. The Society was already provided with a ten-feet zetiith SeEtormade by Mr. SIS- 8Q -fwmied with an acSomatic objeA afs, the principal inkrument requiftte for this experimenty the fame which I took with me to StW Helena in the year I76I; rhich wanted nothing to make it an excellent inficrument bue to have the plumb-linemade adjuflcable,fo aN to paEs before arld bifeEt a fine pOillt at the centre of the infirument. This was ordered to be done, and a nesr wooden Rand provided for it, capable of procuring a mokion of the Sedcor about a vertical axis, by means of which it could be more eafily lrought into the plane of the meridiant t S°t 3 ridian or turned hif round for repeatitlg the obErva tsonswlth theplarxeofthe mfirument placed thecontrary way, in order to find the error of the line of collimation. A large parallelopiped tent, ISa feet Square and I7 feet high, was alfo provicled for nzeltering both the infirument and the obSerarer who Illould uSe it,-compoSed of joices of wood well framed together, and covered with painted anvas. The Society was lilewife poSeffied of moIt of the other inkruments requifite for this experi ment; as an affrmical quadrant and tranfit inficrument made by Mr. BIRD, and an alinomical clock by SHELTONt whi had S i pmsiF on occafion of the obatils of the trmIRt of Venus in I76I or I 769* A theodelite of the beff fiOlt was wmting, a neceffiary in-Parvlment br ol*ainirxg ti figure and dimenfions of the hili. 0ne of Mrv RANSDEN'S wnkrudwn of g inchesdia-meter9 W3S thou«t the fitteic for tl}e purpofe, on account of the excellence of the pla;n on which tt was made, and dwe number of its adjirments being capable of meafuring angles for the moR part to the exadtlzefs of a fingle menute. The other ln{hummts prepared for thi& bufs nefs were, two batorneters of M.0 DE LUC'S wndions made by Mr. PEAIRNE, a nmmwL (knteSs chain; a roll vf painted tape thr-ee poles long, having feet and inches marled upon it; txvo fif poles of zo feet each and four wooden flcands, fw l;apporting th-em when uSed in meafuring the bais, and a br2iZs Itandard of five feet for adjufling th-emr The poles and I}wds were providecl on the bot. Although [ ] Although accounts had been received from various perfons of feveral hills fuppofed proper for the intended purpofe, fome better and fome worfe authenticated; yet, ill order to be fiure of i:inding the beflc hill for the experiuent, it was (letermined to rend a perfon furniShed with prol?er inRruments, to make fuch obServations ollvaxious hills in Englarid and Scotland, as might enable us to cllooSe the fitteR for the purpofe. Accordingly Mr. tHARLES AMASON, who had been employed on feveral aStronomical occafions by the Royal Society, vas appointed to make a tour through the Highlands-of Scotland in the fummer of the year I 7 7 3, taking notice of the principal hills inEngland which layin his route either in his going or in his returax It appeared from his obServations, that fcarce any hill was fo well adapted to the purpoSe as OU1' fanpine hopes hAad led us to expeEt; for either they vere not high enough, or not fllfficiently detKhed from other hills, or their greateR length fell in a wrong direction, too near the meridian, inilead of lying nearly EaR and Wefc,-which is a circutnfiance requifite to make a hill of a given height afford the greatefc effeA of attraction. In pticular, the hills on the confines of York-Shire and Lancaffire, mentioned in the foregoing propo fal, were found rlot to anfwer the defcriptiorl thwat ha(l been given of them. Fortunately, however, E'erthlhire afforded us a remarkable hill, nearly in the centre of Scotland, of fufficient height, tolerably detached from <)ther hillsX and couflderably larger from Eafc to Wefi than from North to South, called by the people of the * 10Xv * .a11 -filence E s%9 ] Erence of latiNde between the tvo frations of the o13fer-J /@ R @ J/ @@ ratory, comes out 54,I, 54,7, 54,o} 55,4, 55o, 5sxo, " ), .. .. 5t,2, s4,o, 54,3, 53xT, ref42ively; the mean of all " which is 54,; the greateflc difference of any one reftllt frorn the mean being only 'w. In like manner, by fingle obfiervations of as many Itaxs; r?z. jB and a Gaffiepeae; £ UrfX majoris; XB, 39, 46, o, 49, and 53 Dracorsis; and X 3 Cygni; made on both fides of the hill, svith the plane of the feEtor facing the Eak; after making a11 the a1lowances as bEfore, colnes out 54,5j 5t,3, 56,82 5325> 54>5, 57X2 56>IX 8 /R J 55,3, 54,I, SS,I, refpeEtively; the mean of all +^rhich is 5 5"; the greateAt (lffererlce of any orle refult from the .. .. mean being 28. Thet^romeans 54, arld ss,o differ , . .. only o,8, which Illould arglle only an alteration of o,4 in the line of coltimation; but this is too fmall a quail-