luidity, and by the energy of the wind. Thus, because fresh water is
considerably lighter than salt, a given wind will produce in a given
distance for the run of the waves heavier surges in a lake than it
will in the sea. For this reason the surges in a great storm which
roll on the ocean shore, because of the wide water over which they
have gathered their impetus, are in size very much greater than those
of the largest lakes, which do not afford room for the development of
great undulations.

To the eye, a wave in the water appears to indicate that the fluid is
borne on before the wind. Examination, however, shows that the amount
of motion in the direction in which the wind is blowing is very
slight. We may say, indeed, that the essential feature of a wave is
found in the transmission of impulse rather than in the movement of
the fluid matter. A strip of carpet when shaken sends through its
length undulations which are almost exactly like water waves. If we
imagine ourselves placed in a particle of water, moving in the
swayings of a wave in the open and deep sea, we may conceive ourselves
carried around in an ellipse, in each revolution returning through
nearly the same orbit. Now and then, when the particle came to the
surface, it would experience the slight drift which the continual
friction of the wind imposes on the water. If the wave in which the
journey was made lay in the trade winds, where the long-continued,
steadfast blowing had set the water in motion to great depths, the
orbit traversed would be moving forward with some rapidity; where also
the wind was strong enough to blow the tops of the waves over, forming
white-caps, the advance of the particle very near the surface would be
speedy. Notwithstanding these corrections, waves are to be regarded
each as a store of energy, urging the water to sway much in the manner
of a carpet strip, and by the swaying conveying the energy in the
direction of the wave movement.

The rate of movement of wind waves increases with their height.
Slight undulations go forward at the rate of less than half a mile an
hour. The greater surges of the deeps when swept by the strongest
winds move with the speed which, though not accurately determined, has
been estimated by the present writer as exceeding forty miles an hour.
As these surges often have a length transverse to the wind of a mile
or more, a width of about an eighth of a mile, and a height of from
thirty-five to forty-f