It is so natural to suppose that to a body falling in the air under the influence of gravity, it is indifferent whether a lateral motion is impressed upon it or not, as regards the time of its fall, that we may sometimes find in elementary text-books the statement that if a ball be shot from a cannon horizontally, at any given height above the ground, and if a ball be dropped vertically at the same instant with the discharge, the two projectiles will reach the ground at the same time, and like illustrations of a supposed fact which has in reality no justification in experience. According to the experiments I am about to describe, this cannot be the case, although it requires another form of projectile to make the difference in the time of fall obvious.

It is shown by the following experiments that if a thin material plane be projected in its own plane horizontally, it will have a most conspicuously different time of falling according to the velocity of its lateral translation; and this time may be so great that it will appear to settle slowly down through the air, as it might do if almost deprived of weight, or as if the air were a highly viscous medium, the time of fall being (it will be observed) thus prolonged, when there is no inclination of the plane to the horizon a noteworthy and unfamiliar fact, ^[*] which is stated here on the ground of demonstrative experiment.