756 Mr. Hutton’s Calculations to- afcertain 
above manner for one of the obfervatories, namely, the 
Northern one, with the places of all or moft of the 
points which fall within this part of the ground, accu- 
rately laid down and marked with dots, as alfo fuch of 
the included letters as have been before mentioned in 
this paper? 
In this plate rabcd, &c. is the chain of ftations 
around the hill; n and K are the Weft and Eaft cairns on 
the extremities of the ridge of the hill ; o the Southern 
obfervatory, and p the Northern one. Of this kind were 
made two large plans, one divided for each obfervatory, 
from which were eftimated the mean altitudes of the pil- 
lars erected on the fpaces into which they are divided. 
Thefe altitudes are eafily eftimated when feveral of 
the points fall near and in the fmall fpaces or bafes, efpe- 
cially when they are near the middle of them ; but, nu- 
merous as the points are, there are evidently many bafes 
in which none at all are contained, nor even near them. 
This circumftance at firft gave me much trouble and dif- 
fatisfa&ion, till I fell upon the following method by 
which the def'edt was in a great meafure fupplied, 
and by which I was enabled to proceed in the eftimation 
of the altitudes both with much expedition and a confi- 
derable degree of accuracy. This method was the con- 
necting together by a faint line all the points which were 
of 
