573 
figure of the earth. 
figure of the earth, theory and observation are in perfect 
agreement. If the arcs which have been measured were no 
longer than that in Sweden, or even than that in England, I 
should not hesitate in attributing to errors of observation and 
local attraction a considerable part of the discrepancy. And 
had the theory been confined to terms of the first order, I 
should have thought it probable that terms of importance 
might be omitted in the second and higher orders. But it 
appears that with the improved theory, applied to the com- 
parison of the Indian and French arcs, the shorter of which 
has an amplitude of nearly ten degrees, it is impossible to 
establish any agreement with the pendulum observations of 
Captain Sabine ; and I know no other series which for 
extent and other advantages can be compared with those. 
The measures of arcs of the meridian which have hitherto 
been made are, I imagine, insufficient for the determination of 
the figure of the earth. The arcs in India and France are 
the only ones in which the possible errors in latitude would 
not bear a sensible proportion to the effects of ellipticity. 
Captain Sabine has proposed to measure an arc in Spitzber- 
gen. The shortness of the arc, and the mountainous cha- 
racter of the country, would make it almost useless. The 
desideratum at present is an extensive arc in a high latitude. 
We have two good arcs near the equator ; of which the 
Indian, at least, is as long as can be desired. We have a 
still longer arc almost exactly bisected by the parallel of 45 0 . 
With an arc of equal length in the neighbourhood of the 
pole. we might determine the three terms in the expression 
for an arc of the meridian to great accuracy. This perhaps 
it will be impossible ever to execute. 
4 E 
MDCCCXXVI. 
