The Account of a 
528 
since the differences are, excepting two instances, constantly 
minus ; this, however, presupposes that the degree of the great 
circle perpendicular to the meridian in lat. 50° 41', as we have 
found it, and likewise the degree upon the meridian arising 
from the measured arc between Greenwich and Paris, and their 
difference in latitude, are nearly right. Also, were it of Mr. Bou- 
guer's figure, the degree of a great circle in lat. 50° 41' would 
be 61270 fathoms, which is 88 fathoms greater than we have 
derived it ; we may therefore safely infer, that his hypothesis 
is more ingenious than true ; since it cannot be supposed that 
the degree, resulting from these observations, is 88 fathoms in 
defect ; but whether the earth be a figure formed by the re- 
volution of a meridian round its axis, upon which the length 
of the degrees increase according to any law, or one whose me- 
ridians are formed by the combination of many different curves, 
it appears to be certain, that we may consider 61 182 fathoms 
as nearly the length of a degree of a great circle, in latitude 
50° 41', by which we are enabled to settle the longitudes of 
those places whose situations have been determined in this 
operation. 
The length of the degree, as given by General Roy, from 
the directions of the meridians at Botley Hill and Goudhurst, 
is 61248 fathoms, which is 66 fathoms different from this re- 
sult : but this is not to be considered as extraordinary, since 
the distance between those places is not more than 23 miles, 
and the direction very oblique to the meridian. It is an in- 
dispensable requisite, that the stations chosen for this purpose 
be nearly east and west ; because if both places were on the 
same parallel of latitude, the horizontal angles would give the 
difference of longitude, without adverting to the principle of 
