the mean 'Denjity of the Earth. 715 
puted lines, both thofe above-written and others, and 
they were generally found to agree very exactly, accord- 
ing to the fcale by which the plan was conftrudted. The 
ufe of this large map was to receive and admit of the 
diftindt and accurate exhibition of the figures in their 
true places, exprefling the number of feet in elevation or 
depreflion with refpedt to each obfervatory of every 
point and fedtion of the ground whofe elevation or 
depreflion might be obferved. But before I proceed to 
the computation and conftrudtion of the points in the 
fedtions, I fhall here abftradt the numbers which exprefs 
the relative elevation of the principal original points in 
the furvey, being the extremes of the lines whofe lengths 
are above abftradted. Thefe few numbers are the refults 
of the calculation of feveral hundreds of triangles con- 
ceived in a vertical pofition, their bafes being either the 
horizontal lines above-written, or other lines drawn as 
diagonals between many diftant points in the furvey, ac- 
cording to the number of vertical angles which had been 
obferved; and of thefe bafes, whether real or imaginary, 
each generally afforded two vertical triangles, as the 
angles of elevation and depreflion were taken alternately 
at both ends of the lines. It is fcarcely neceflary to re- 
mark, that all thefe triangles are right-angled, the com- 
mon bafe being one of the fides about the right angle, 
and the other the difference in altitude between the two 
