4i© Major-General Roy’s Account of the 
ficient to prove the great excellence of the chain, although 
another will be given hereafter hill more furprifmg. 
On the fame day that the fecond fedtion 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 unneceffary. It will be fufficient to fay, that the 
fpirit level made ufe of on this occafon was a very good one, 
about eighteen inches in length, and could at all times be very 
readily and accurately adj ufted by inverfion in its Y’s. The tops 
of the pickets, marking the hypothenulal diftances, were the 
points on which the levelling rods were placed on each fide of 
the level ; which being inverted at the intermediate picket, 
points equi-diftant from the center of the earth were thereby 
obtained, at the crofs vanes of the levelling rods, and no cor- 
rection for curvature or refraCtion necefifary. It will be readily 
underftood, that the relative heights of the pickets were found 
by meafuring their diftances from the centers of the crofs 
vanes and axis of the telefcope refpeCtively. 
The fix firfl; columns towards the left-hand of the 
frit or general table fubjoined to this Paper, fihew dif- 
tinCtly every thing relating to the levels of the whole 
bafe, thofe of the third fedtion having been determined 
on the 2 2d of June. By examining the table it will be 
feen, that the afcent on the firfl: fection is io-555 feet, 
on the fecond . 8.580 
and on the third . 12.130 
Total . . 31.265 feet, be- 
tween the lower extremity at Hampton Poor-houfe, ^and the 
higher near King’s-Arbour.. 
The 
