impelling power of the man's muscles. Any one who will expose his body
to this blow of the surf will recognise how violent it is; he may, if
the beach be pebbly, note how it drives the stones about; fragments
the size of a man's head may be hurled by the stroke to the distance
of twenty feet or more; those as large as the fist may be thrown clear
beyond the limits of the wave. So vigorous is this stroke that the
sound of it may sometimes be heard ten miles inland from the coast
where it is delivered.

Moving forward up the slope of a gently inclined beach, the fragments
of the wave are likely to be of sufficient volume to permit them to
regather into a secondary surge, which, like the first, though much
smaller, again rises into a wall, forming another breaker. Under
favourable conditions as many as four or five of these successive
diminishing surf lines may be seen. The present writer has seen in
certain cases as many as a dozen in the great procession, the lowest
and innermost only a few inches high, the outer of all with a height
of perhaps twenty feet.

Along with the direct bearing action of the surf goes a to-and-fro
movement, due to the rushing up and down of the water on the beach.
This swashing affects not only the broken part of the waves, but all
the water between the outer breaker and the shore. These swayings in
the surf belt often swing the _debris_ on the inner margin over a
range of a hundred feet or more, the movement taking place with great
swiftness, affecting the pebbles to the depth of several inches, and
grinding the bits together in a violent way. Listening to the turmoil
of a storm, we can on a pebbly beach distinctly hear the sound of the
downward stroke, a crashing tone, and the roar of the rolling stones.

As waves are among the interesting things in the world, partly on
account of their living quality and partly because of their immediate
and often exceeding interest to man, we may here note one or two
peculiar features in their action. In the first place, as the reader
who has gained a sense of the changes in form of action may readily
perceive, the beating of waves on the shore converts the energy which
they possess into heat. This probably warms the water during great
storms, so that by the hand we may note the difference in temperature
next the coast line and in the open waters. This relative warmth of
the surf water is perhaps a matter of some importance in limiting the
development of