407 
of an Arc of the Meridian . 
edge of a very strong plank, having its axis horizontal, and the 
pivots resting in Ys firmly fastened in the middle. The end of 
the arch, whose face became vertical, was supported by a brass 
plate screwed down on the end of. the plank. When the pivots 
were placed in the Ys, and the telescope sustained in several 
places, to keep it from bending, a brass slider, on the surface 
of the plank, was moved till the line before mentioned coin- 
cided with that described on the arch. The telescope was then 
quickly taken out of the Ys, and, as speedily as possible, brought 
into a similar position on the other side; for which purpose, 
braces to support the tube had been previously prepared. By 
these means, twice 'the length of the radius was obtained ; 
proper care having been taken to have the Ys so placed, that 
the centre of the pivots should be in the same plane with the two 
sliders at the extremities of the plank. The distance between 
the lines was then measured, and ~ taken for the chord of 
7° io', which was immediately laid off on the face of the sector, 
on both sides zero. 
Although little doubt could be entertained of the truth of the 
total arc thus assumed, yet, that the length of its chord might be 
compared with that derived from the usual modes of operation, 
Mr. Berge ( as proposed by Mr. Ramsden ) prepared a brass 
arch, which he let into a frame, on which, after striking a por- 
tion of a circle with the radius obtained as above, he laid off the 
chord of 6o°. This arch he divided by continual bisection, till he 
obtained the chord of 7 0 io', which he compared with the same 
angle laid off on the sector's limb. He had the satisfaction of 
finding no perceivable difference ; and, that there really existed 
none, was denoted by the unresisted fall of the points into 
their respective holes. The arch of the sector was then divided 
S G 2 
