Since a body falls to the ground in consequence of the earth’s
attraction on _each_ of its molecules, it follows that, all other
things being equal, all bodies, great and small, light and heavy,
ought to fall with equal rapidity, and a lump of sand without cohesion
should during its fall retain its original form as perfectly as if it
were compact stone. The fact that a stone falls more rapidly than a
feather is due solely to the unequal resistances opposed by the air to
the descent of these bodies; _in a vacuum all bodies fall with equal
velocity_.
_In a vacuum, however, liquids fall like solids without separation
of their molecules._ The _water-hammer_, a model used in scientific
schools, illustrates this: the instrument consists of a thick glass
tube about a foot long, half filled with water, the air having been
expelled by ebullition previous to closing one extremity with the
blow-pipe. When such a tube is suddenly inverted, the water falls
in one undivided mass against the other extremity of the tube, and
produces a sharp metallic sound, resembling that which accompanies the
shock of two solid bodies coming suddenly together.
NOTE.—The resistance opposed by the air to falling bodies is
especially remarkable in the case of liquids. The Staubbach in
Switzerland is a good illustration; an immense mass of water is seen
falling over a high precipice, but before reaching the bottom it is
shattered by the air into the finest mist. See Parker’s Philosophy,
pp. 69-70.
It has been ascertained, by experiment, that from rest, a body falling
freely will descend 16-1/12 feet in the first second of time, and will
then have acquired a velocity, which being continued uniformly, will
carry it through 32-1/6 feet in the next second. Therefore if the
first series of numbers be expressed in seconds, 1″, 2″, 3″, &c., the
velocities in feet will be 32-1/6, 64-1/3, 96-1/2, &c.; the spaces
passed through as 16-1/12, 64-1/3, 144-3/4, &c., and the spaces for
each second, 16-1/2, 48-1/4, 80-5/12, &c.