402 On the Velocity of Air. 
The second experiment by the same process 
gives 361.6 feet per second. If we would com- 
pare these together, we may say, as the square 
root of 30, the head, is to 233.3 the velocity ; so 
is the square root of 72, the second head, ta 
361.8 feet the velocity per second. 
Again:—As the square root of 6 feet, 1s to 
 361,6; so isthe square root of 33 feet, to 845.2 
feet per second, the velocity produced by that 
head; or the initial velocity with which the 
atmosphere would enter a vacuum, This velocity 
found by experiment is 487 feet per second less 
than has been assigned by theory, 
It appears however that the results as deter- 
mined by theory and experiment do not differ 
more than in the case of effluent water. For, if 
we would reduce the velocity of effluent water, 
found by theory to that which experience gives, 
we must multiply it by ,634. Accordingly, if 
we muluply 1932 feet, the velocity of the atmos- 
phere entering a vacuum, as calculated above by 
3634, the product is 844.5 per second, differing 
but zo of a foot from that just found by 
experiment. 
I have also made experiments by sinking vessels 
in water, till their tops were even with its sur- 
face, and opening the aperture that the rising 
water might expel the air, by which I obtained 
