FROM THE ORDNANCE TRIGONOMETRICAL SURVEY. 
625 
which in terms of p and q, are — 
601 ISO^j 
TT 
IOOOOttV^ 6V“ 
599 180^, 
TT 
] — 
180^. 
'IOOOOtt 
(^'+V%)+ 
If we put 4 for the mean error of an equation. 
Mean error of /?+^S' = 29 l^V^ 1267‘24-2587>^+ 1 15’3X®. 
Now the sum of the squares of the errors, or quantities x, is 160‘26 ; 
/ 2y^ = + 2-48. 
V 38-12 ~ 
The values of a and h, and their mean errors, are consequently 
a =20924933 ; mean error +800 
6 = 20854731 ; mean error +606. 
The ratio of the axes is expressed by the relation 
" • " " 2n ~^ 2 ■ 2n 2 
4 = 300 - 30 ?+ 3 ?^ 
Consequently the compression is 
a — b 1 
a ~298-07’ 
mean error of denominator +2'70. 
The length of a degree of the meridian whose mean latitude is X, is consequently 
= 364596-61 — 1837-79 cos 2X+3-85 cos 4X, 
and the length of a degree of longitude in latitude X 
=365515-56 cos X— 306-96 cos 3X+0-39 cos 5X. 
Had the point Evaux in the French Arc, at which there is obviously some peculiar 
local disturbance, been omitted, we should have obtained p= — 1 -65000, q= +-09341 : 
these values would have increased the values of the semiaxes as obtained above by 
about 200 feet each, and increased the compression to 
a — b 1 
“^“297-72' 
The corrections in the French Arc would then stand thus : — 
Formentera . 
. . . +1-319 
Mountjouy . 
. . . +3-788 
Barcelona 
. . . +0-434 
Carcassonne , 
. . . —1-246 
Pantheon . . 
. . . — 3-457 
Dunkirk . . 
. . . —0-839 
and the correction for Evaux is increased to 
8-059. 
The corrections for the other 
arcs are not materially altered, but are in general diminished; the mean error of the 
