On the Velocity of Air. 399 
an equal column of water, yet the weight of the 
particles to be projected is greater in the same 
ratio. Onthe other hand, if air is lighter than 
water, the particles projected are also lighter in 
proportion. Ifa tube 16 feet high be filled 
with air of any density, that air, like water, would 
flow into a vacuum with a velocity of 32 feet per 
second, no corrections being made for resistance.* 
And if we take the gravity of air to water as 
1 to 840, then a column of one foot of water, 
compressing air, will produce as great a velocity 
in that air asa column of air 840 feet high, sup- 
posing it was of uniform density. 
If we take the whole pressure of the atmosphere 
equal to 33 feet of water, or its height (supposing 
it to be equally dense, which in this case will make 
no difference) equal to 33 multiplied by 840, or 
27720 feet. Then as the square root of 16, is to 
32, the velocity at that depth ; so is the square root 
of 27720, to 1332 feet per second, the initial 
velocity of the atmosphere into a vacuum. 
* In the supposition of a perpendicular tube open at 
the top, filled with air or any elastic fluid, the author 
takes the density of the column at the bottom or where 
the aperture is made, to arise solely from the weight of 
the elastic column ; and the altitude to be that which 
would be if the whole column were reduced to the 
density of that at the bottom. 
VOL. V. L 
