in order to af certain the height of Mountains. 547 
To collect thefe laft experiments in one point of view. 
Feet. 
The 1 ft feries gives for the error on every 1 000 ft. 
4th, — — — 
5th, — — — 
6th, — — ■ — 
( 8 . 7 
1 6.9 
22.8 
23-5 
23.1 
25.2 
The mean error, 
21.7 
which agrees within two feet in a thoufand with the de- 
termination on Mont Saleve. This refult then juftifies 
my conclufion (in p. 556.) and proves that either the 
proportional gravity of air and quickfilver is now dif- 
ferent from what it was, when M. de luc made his 
experiments, viz. from 1756 to 1760; or that his or 
my obfervations are defective. That my trigonometrical 
meafurements were fufficiently exa£t, viz. to within two 
or three feet, I think I have already fliewn ; and even that 
his were alfo. Within what limits my barometrical er- 
rors are to be found is not difficult to determine from 
what has been before premifed. That the fcale of Mr. 
de luc’s barometer was lefs accurate than mine, is, I 
think, without a doubt; and indeed he never attempted 
a divifion lefs than ^th of a French line, or about 
4 B 2 °f' 
