H2 Mr. Pictet’s Confederations on the 
Should the method, propofed by the late General Roy 
for afcertaining the length of the parallel independently of 
aftronomical obfervations, be adopted, it might be carried into 
execution with no great difficulty from the fummit of the fame 
mountain, where we juft now fuppofed the fignal by the In- 
dian lights to be placed. 
The triangles relative to the meafurement of the parallel 
make but one fuite with thofe of the meridian, and there are 
four very convenient places along the fame parallel for mea- 
furing bafes of verification. They are perfectly level plains, 
forming the bottom of the valley through which the Rhone 
flows between the towns of Aigle and Villeneuve , and between 
Martigny and Sion. Their relative fituations are roughly indi- 
cated in the map. The above general confiderations, together 
with the particulars which are fubjoined to the fketch, feem to 
ascertain the full prafticability of the enterprize. May I be 
allowed to add a few refledlions on its conveniency ? 
The re-union of the two meafurements (of latitude and lon- 
gitude) in the fame fpot, is an advantageous circumftance; 
and the more fo, if we confider that this fpot lies between the 
45 and 46th degree, that is, in the mean latitude between the 
pole and equator, near which latitude the mean radius of the 
earth takes place in the well-founded fuppofition of its being a 
fpheroid. This radius, found by the moft accurate meafure- 
ment hitherto attempted, would become a ftandard, and to 
which the refults of the equatorial and northern meafurements 
being compared, the true figure of the earth would be the 
better afcertained. 
The pofition or relative longitude of the meridian of Geneva 
iswell determined by a great number of obferved immerfions 
# Phil. Tranf. 1787, p. 216. et feq. 
5 
and 
