4j5$ The Account of a 
of a new base, not only to verify tHe triangles remote from 
Hounslow Heath, but likewise to determine the sides of those 
which might be hereafter projected for the survey of the 
West of England. The situation which we had looked for- 
ward to, as being the only one which would afford a base line 
of sufficient extent, was Sedgemoor in Somersetshire, not hav- 
ing then imagined that any place could be found fit for the 
purpose to the eastward of that situation. 
By maturely deliberating upon the steps to be taken for this 
necessary business, it soon appeared, that Sedgemoor, from its 
remoteness, would not suit for a base, which was intended to 
be applied as a test to the sides of the great triangles which 
were now constituted. Inquiry was therefore made after a 
spot which might be less exceptionable ; and as information 
was obtained that Longham Common, near Poole in Dorset- 
shire, was likely to afford such a base, we examined it in the 
January of this year ; but not finding it fit for the purpose, 
we proceeded to Salisbury Plain, where we found that a base 
line of nearly seven miles might be measured without much 
difficulty between Beacon Hill, near Amesbury, and the Castle 
of Old Sarum. With respect to the nature of the ground, as 
any observations concerning it will be introduced with more 
advantage when we treat of the particulars of the measure- 
ment, it will be only necessary to observe, that prior to de- 
termining upon the possibility of measuring it with the ne- 
cessary accuracy, we considered of the errors which would be 
likely to creep in from the many hypotenuses which the base 
would consist of, and from other circumstances which the 
ground from its inequality might be supposed to produce. 
As the principal object of this year's business was, to deter- 
