VOL. LVIII.] PHILOSOPHICAL TRANSACTIONS. 5^ 



to the vertical wires, as a point in the meridian. And the time of stars passing 

 an azimuth in the direction of the line ab, for determining the angle bam, was 

 found by bringing the vertical wire in the telescope to bisect a candle placed, 

 about 1^ mile from a, in the line ab; the telescope was then elevated to the 

 star, and the time when it passed the said vertical wire taken. 



The observations for determining the meridian am, and the angle that the line 

 AB makes with the said meridian, were then sgt down. At the instant when 

 the clock showed 22*' 53*" 30^, the vertical wire was brought to bisect the star * 

 Ursa major; and then the vertical axis was made fast (the level showing the 

 horizontal position of the axis of the telescope and the line of collimation being 

 just), the telescope was then brought down to the horizon, and by means of a 

 candle seen through a small hole in a board, a mark at the distance of 

 21 cha. 42 lin. was placed in a line with the said vertical wire. In like manner, 

 when y Ursa majoris, and the pole star passed the meridian, as known by the 

 clock, the vertical wire was brought, at those instants of time, to the said stars, 

 and the telescope turned down to the horizon, in the same manner above- 

 mentioned, and the wire bisected the candle, when held to the 1st mark, as 

 near as could be judged. At 2'' 57"* 10-^' |3 Ursa minor was bisected by the 

 vertical wire for finding a meridian; and the telescope then turned down to the 

 horizon, and by bringing a candle at the distance of a mile, to be bisected by 

 the vertical wire, we there placed a mark. After these observations, the clock 

 was wound up, in doing which it was stopped about 23^ 



Again at 2*' 58' 41" the wire was brought to (3 Ursa minor for finding a 

 meridian as before; and, by means of a candle at the distance of a mile, a mark 

 was placed, which fell 3 inches east of that placed the 14th. In this last 

 observation the axis of the telescope was turned end for end; that is, the 

 telescope itself was turned upside down. This proved the ends of the cylinder 

 to be good. 



On the 17, in the evening, by means of a candle placed behind a board, with 

 a small hole in it over the mark placed the 13th instant, the line was extended 

 to the marks at a mile distance, and there a mark placed, which fell ^ of an inch 

 east of the mark placed the 14th instant. 



From the whole, there are 6 observations, all within the space of about 3 

 inches, at the distance of a mile: The mean was taken as a point in the 

 meridian, north of the point a. At this meridian point m, we laid ofi^ the line 

 mp at right angles to the meridian a, m, m, and, by a candle being placed at o, 

 in the right line ab, about 1-J- miles from a, another candle was advanced along 

 the line mp, till the vertical wire in the telescope bisected both candles: Under 

 the candle, at the intersection of mp, with ab, viz. at p, a mark was placed in 

 the ground. The ground between m and p being made smooth (it was level 



VOL. XII. 4 D 



