the mean Denjity of the Earth. 723 
But nearly the fame faving in the great labour of 
computation would be made if the vertical and horizon- 
tal angles had both been taken at the end of the bafe 
fartheft from the beginning of the fedtion. And this 
method would alfo be much the eafieft in making the 
furvey on the ground, as there would then need only one 
obferver with an inftrument to meafure both horizontal 
and vertical angles ; and any perfon, without an inftru- 
ment, could diredt in a line the perfon who moves and 
places the poles, or he may even diredt himfelf after his 
firft pole has been placed, by means of a back objedt, as 
is commonly done -in land furveying. 
Of this kind there happens to have 
been one fedtion taken, proceeding 
from g, and making with gp an angle 
of 85°, p being the Northern obfer- 
vatory, and where both the bearings 
and depreflions of the points p in the 
fedtion line were obferved. 
p 
i8o r 
4 - a = 85 
Z.p+£/>= 95 
Log. 1 
pg 368262 I i s a conftant number from which 
^ 34 t he fi nes D f p in the fifth column are 
Sum 3'68 o96 1 to be dedudted. 
4 U 2 
Poles. 
