THERMOMETRICAL OBSERVATIONS. 2u 



From the refult of the above obfervations it appears that the obfervatory 

 ■was 16". 26 or ab"ut one dioufand, fix hundred and forty-four feet and 

 eight-tenths of a foot Englilh meafure too f.ir ibuth, which diftance was 

 laid off to the nortli on a meridional line drawn Irom the obfervatory O to 

 the point A, (fee Plate V. Fig 4.). The point A is in a deep hollow, or chafm. 

 — From the point A a viila was opened both to the eaft and well, and as 

 near at right angles to the meridian as poffible : but the point A being too 

 low for doing it with certainty, the elevated pofition B eaft from A, and 

 dillant thirty-tour perches, was pitched upon as the moft proper place for 

 commencing our operations. The traniit inftrument vras according-y put 

 up at B, and the peipendicular or vertical fibre of the telcfcope, was 

 brought to defcribe the prime vertical by taking equal altitudes of Arfturus. 

 — This was effected in the following manner : a piece of timber T, flatted 

 on the upper fide, was placed at -die point C, diitant fr m B feventy-one 

 perches, and at right angles to the vifta ; on this piece of timber at U, one 

 of tlie copper lanterns already defcribed was placed on the iSth in the af- 

 ternoon ; the tianfit inlf runient b:ing previoufly adjufted, and the vertical 

 fibre which was a fingle thread of fpider's web, being brought to bife<£t 

 the aperture in the front of the lantern. — A few minutes before the ftar in 

 its afcent was expected to appear in the field of the telefcope, it was elevated 

 about forty-one and an half degrees : immediately upon the (lar's making its 

 appearance, the horizontal fibre of the tel=fcope was brought to bifed it, and 

 kept upon it by gradual'y elevating the inftrument until the ftar arrived at 

 the interfection of the fibres, at that inftant the elevating arc was faftened, 

 and afterwards the clamp of the perpendicular axis was loofened. On the 

 morning of the 19th, the level of the inftrument was carefully examined and 

 adjufted. A Ihort time before the ftar was expected to appear in ;he field of 

 the telefcope, in its defcent, the telefcope was directed weft : as foon as the 

 ftar appeared in the field, the c'.amp was iaftened and the vertical fibre brought 

 to bifeft the itar, and kept upon it by the fcrews which dire«ft the arm of the 

 clamp until it arrived at the interfeifiion of the fibres^ — The elevating ate was 

 then loofened, and the telefcope taken out of the Vs and revcrfed ; a li«-hted 

 candle having been previoufly put into ar.other l..ntem fimilar to the nrft, 

 and placed on the fame piece of timber. The aperture of the fecond lan- 

 tern was brought into the direvftion of the vertical fibre (which fuppofe 

 to be at n) by an affiftant at C, who received the necelTiiry fignals for 

 that purpofe from the obferver at B. — In the forenoon of the fame day the 

 <diftance between the apertures of the two lanterns v/as carefully bifeiTted, 



which 



