488 The Account of a 
Hill, in order to have a view of Long Knoll, near Maiden 
Bradley, and Inkpin Beacon towards Hungerford. 
We shall now close this section by observing, that the mea- 
surement of this base has been almost without an alternative, 
since Sedgemoor, the only spot west of Salisbury proper for 
an operation of this kind, is about to be inclosed. Therefore 
had we not adopted this expedient, the triangles which may 
hereafter be carried on to the remote parts of the west of Eng- 
land, would probably have depended on the Hounslow Heath 
base. But we are led to believe, that this base has been mea- 
sured with nearly the same accuracy which would have at- 
tended the operation, had the ground been nearly level ; since 
there is a certainty of the angles, formed by the hypotenuses 
and the plane of the horizon, being determined within a mi- 
nute of the truth. Now if an error of a minute in those incli- 
nations, supposing them all to lie the same way, produce only 
that of three inches in the whole base, it may be concluded 
that 36574,4 is very nearly its true length. 
SECTION FOURTH. 
Calculation of the Sides of the great Triangles. 
art. 1. Of the Division of the Series into different Branches. 
In order to methodize the contents of this section, it has 
been considered as proper to divide the series into different 
branches, as the triangles of wdiich they are composed seem 
naturally to resolve themselves into distinct classes. 
The first branch, is that which immediately connects the 
