766 Col. roy’s Experiments for 
would be obtained with certainty. Suppofing, forin- 
ftance, Ben Nevis was divided into four feCtions, five ba- 
rometers, with as many obfervers, would be neceflary. 
This number may feem great, but the expence of peo- 
ple employed in that way would be inconfiderable. And 
if it fhould be judged proper, there could not furely be 
any great difficulty in providing reafonable accommoda- 
tion for an obferver, who fhould live a whole year at the 
top of the mountain, while another made correfponding 
obfervations below. 
But the perfecting of the theory of the barometer is not 
the only advantage that would accrue from a combina- 
tion of thefe obfervations; for, while they were carry- 
ing on in different climates, or zones of the earth, good 
opportunities would offer of determining the refractions, 
as well as the force of gravity and figure of the globe, 
from the vibrations of the pendulum. 
The mean expanfion of common air is already found 
to be greater than what was formerly fuppofed ; where- 
fore the mean refraCtion will be altered proportion ably. 
And fince the expanfion of moift air is found to be fo 
much greater than that of common air, a larger field for 
inquiry and inveftigation is now laid open. 
With refpeCt to the experiments with the pendulum, 
Mr. bouguer feems to have been the only perfon, fo far 
as 
