420 Major 'General Roy's Account ^f the 



flcient to prove the great excellence ot the chain, althougli 

 another will be given hereafter ft ill mce furpriliiig. 



On the fame day that the fecond fedlion of the bafe was 

 meafured, the levels of that and the firft were taken. The 

 operation of levelling is fo univerfally known, as to render any 

 detail of it nnneceilary. It will be fufticient to fay, that the 

 fpirit level made ufe of on this occafion was a very good one, 

 about eighteen inches in length, and could at all times be very 

 readily and accurately adjufted by inverfion in its Y's. The tops 

 of the pickets, marking the hypothenufal diftances, were the 

 points on which the levelling rods were placed on each iide of 

 the level ; which being inverted at the intermediate picket, 

 points equi-diflant from the center of the earth w^ere thereby 

 obtained, at the crofs vanes of the levelling rods, and no cor- 

 reftion for curvature or refra6lion neceflary. It will be readily 

 underftood, that the relative heights of the pickets were found 

 by meafuring their diflances from the centers of the crofs 

 vanes and axis of the telefcope refpeitively. 



The fix firft columns towards the left-hand of the 

 firfl: or general table fubjolned to this Paper, fhew dlf^ 

 tlndly every thing relating to the levels of the whole 

 bafe, thofe of the third fedion having been determined 

 on the 2 2d of June. By examining the table it will be 

 feen, that the alcent on the firfl: fecllon is 10.555 ^^^^> 



on the fecond , 8.380 



and on the third . 12.130 



Total . . 31.265 feet, be- 



tween the lower extremity at Hamptoi\ Poor-houfe, and the 

 higher near King's- Arbour. 



The 



1 



