does not move. If it did, when a stone is thrown into a pond and
the ripples spread away in an ever widening circle, there would
appear at the centre an ever increasing hole. No, the water that
composes the body of a wave is stationary. Thus, you may watch a
particular portion of the ocean's surface and you will see the sane
water rise and fall a thousand times to the agitation communicated
by a thousand successive waves. Now imagine this communicated
agitation moving shoreward. As the bottom shoals, the lower portion
of the wave strikes land first and is stopped. But water is fluid,
and the upper portion has not struck anything, wherefore it keeps on
communicating its agitation, keeps on going. And when the top of
the wave keeps on going, while the bottom of it lags behind,
something is bound to happen. The bottom of the wave drops out from
under and the top of the wave falls over, forward, and down, curling
and cresting and roaring as it does so. It is the bottom of a wave
striking against the top of the land that is the cause of all surfs.

But the transformation from a smooth undulation to a breaker is not
abrupt except where the bottom shoals abruptly. Say the bottom
shoals gradually for from quarter of a mile to a mile, then an equal
distance will be occupied by the transformation. Such a bottom is
that off the beach of Waikiki, and it produces a splendid surf-
riding surf. One leaps upon the back of a breaker just as it begins
to break, and stays on it as it continues to break all the way in to
shore.

And now to the particular physics of surf-riding. Get out on a flat
board, six feet long, two feet wide, and roughly oval in shape. Lie
down upon it like a small boy on a coaster and paddle with your
hands out to deep water, where the waves begin to crest. Lie out