5^9 
Trigonometrical Survey. 
the sums of the angles on a sphere and a spheroid being nearly 
equal, when the places on each have corresponding latitudes, 
and the same difference of longitude. 
Was a degree of a great circle perpendicular to the meri- 
dian measured in some place remote from the latitude of 50° 
41', the diameters of the earth, supposing it an ellipsoid, might 
be determined ; for if l — the length of a degree of a great 
circle perpendicular to the meridian, in the latitude whose sine 
is s and cosine c, and L = the length of the degree in lat. 50° 
41', a and b being the sine and cosine of that latitude ; then will 
the ratio of the axes be that of /f c 1 — L z b z : </ L 2 a 3 — - l z s*. 
It is therefore, much to be wished, that such measurements 
were made in the northern part of Russia, and in the south of 
France, where the methods we have taken to measure this de- 
gree would also be applicable. 
Having given the length of a degree of what may be con- 
sidered a great circle upon the earth's surface, as deduced from 
the observations which have been made at Beachy Head and 
Dunnose, and likewise drawn such conclusions as appear to 
arise from it ; we shall close this section with observing, that 
as the preserving of the points marking these stations has been 
considered of great consequence, his Grace the Duke of Rich- 
, mond ordered an iron gun to be inserted in the ground at each 
of those places, which was done in the autumn of 1794. By 
these points being rendered permanent, the truth of this part 
of the operation can be examined, by re-observing the direc- 
tions of the meridians ; and that this may be done with the least 
trouble, we have preservedthe points, where the staffs were 
erected on Brading Down and the Hill above Jevington, by 
inserting large stones in the ground, having a small hole in 
