486 The Account of a 
In the adjoining figure, let B a, a e, 
e c, and c O be the several hypotenuses, 
or measured lines ; then will the sum 
of the corrections for their reduction to 
the plane of the horizon, as given in 
the table, exhibit that of the differences 
between the horizontal lines, b a,d e,f 
c, h O, and their corresponding hypo- 
tenuses. 
'Again, with the radius CB, C being the centre of the earth, 
describe the arc B I, or that subtended by the base, and 
through the terminations of the several hypotenuses, draw the 
lines C A, C D, G H, and C I ; then will the lines B A, A D, 
D H and H I be those to which the horizontal ones b a, d e, 
f c, and h O are to be reduced, and which may therefore be 
done by the proportions of the lines, C a, C e, C c, and C O, 
to the constant radius C B. Upon this principle, the correction 
0,501 foot has been obtained, and which is the sum of the dif- 
ferences between the lines b a, d e,f c, and h O, and their cor- 
responding ones in the arc B I. 
art. iv. Height of Beacon Hill above the Southern Extremity 
of the Base. 
The sum of the perpendiculars or elevations in Feet, 
the fourth column, is - - 218,6937 
And of the depressions in the fifth column 634,8222 
Therefore the depressions exceed the elevations 416,1285 
The difference of the sums in the seventh and 
eighth columns, is, in feet 
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