The resistance of the air to fallen bodies is not proportioned to the
weight, but depends on the surface which the body opposes to the air.
Now, the feather exposes, in proportion to its weight, a much greater
surface to the air than a piece of gold does, and therefore suffers
a much greater resistance to its descent. Were the guinea beaten to
the thinness of gold-leaf, it would be as long, or even longer in
falling than the feather; but, let both fall in a vacuum, or under the
receiver of an air-pump, from which the air has been pumped out, and
they will both reach the bottom at the same time; for gravity, acting
independently of other forces, causes all bodies to descend with the
same velocity.
[Illustration]
An apparatus for performing this experiment is shown in the engraving:
the coin and the feather are to be laid together, on the brass flap, A
or B: this may be let down by turning the wire, C, which passes through
a collar of leather, D, placed in the head of the receiver.