due to the height of the column of air which would produce the pressure
sustained; and the weight of air being known, as well as the pressure it
exerts on the earth's surface, it becomes easy to tell what height a column
of air, an inch square, and of the atmospheric density, would require to
be, to weigh 15 lbs. The height would be 27,818 feet, and the velocity
which the fall of a body from such a height produces would be 1,338 feet
per second.



VELOCITY OF FALLING BODIES AND MOMENTUM OF MOVING BODIES.

15. _Q._--How do you determine the velocity of falling bodies of different
kinds?

_A._--All bodies fall with the same velocity, when there is no resistance
from the atmosphere, as is shown by the experiment of letting fall, from
the top of a tall exhausted receiver, a feather and a guinea, which reach
the bottom at the same time. The velocity of falling bodies is one that is
accelerated uniformly, according to a known law. When the height from which
a body falls is given, the velocity acquired at the end of the descent can
be easily computed. It has been found by experiment that the square root of
the height in feet multiplied by 8.021 will give the velocity.

16. _Q._--But the velocity in what terms?

_A._--In feet per second. The distance through which a body falls by
gravity in one second is 16-1/12 feet; in two seconds, 64-4/12 feet; in
three seconds, 144-9/12 feet; in four seconds, 257-4/12 feet, and so on. If
the number of feet fallen through in one second be taken as unity, then the