On the Velocity of Air. 403 
the same velocities as above; but the method of 
computing is much more intricate, for which 
reason I shall not insert them. 
From the above, it appears that a pressure 
equal to 93 feet of water, will expel air out 
of bellows into the atmosphere with a velocity 
of 845 feet per second, that one foot of water 
in-depth will produce a velocity of 1474 feet, 
and one inch a velocity of 42 feet per second, 
or 20 miles an hour. . 
Hence we may construct a table shewing 
the velocity communicated to air by any head 
of water. For, as the square root of 6 feet, is 
to the velocity produced by that head; so is 
the square root of any other depth, to the velocity 
produced by that depth. 
We may also, from the above, construct an 
instrument which will shew the velocity with 
which air flows out of any kind of bellows, 
with as much accuracy as the experiments have 
been made, on which its construction depends. 
