liable to beat upon the western and northern coasts in the winter
months than at any other period of the year; whilst the calmest weather
may be expected between May and August.

Waves.

The size of waves depends upon the force of the wind, and the distance
along which it blows continuously, in approximately the same direction,
over a large expanse of ocean. The greatest waves are, accordingly,
encountered where the maximum distance in a certain direction from the
nearest land, or, as it is termed, the "fetch," coincides with the line
travelled by the strongest gales. The dimensions, indeed, of waves in
the worst storms depend primarily on the extent of the sea in which they
are raised; though in certain seas they are occasionally greatly
increased by the exceptional velocities attained by hurricanes and
typhoons, which, however, are fortunately restricted to fairly well
defined and limited regions. Waves have been found to attain a maximum
height of about 10 ft. in the Lake of Geneva, 17 ft. in the
Mediterranean Sea, 23 ft. in the Bay of Biscay, and 40 ft. in the
Atlantic Ocean; whilst waves of 50 to 60 ft. in height have been
observed in the Pacific Ocean off the Cape of Good Hope, where the
expanse of sea reaches a maximum, and the exposure to gales is complete.
The length of large waves bears no definite relation to their height,
and is apparently due, in the long waves often observed in exposed
situations, to the combination of several shorter waves in their onward
course, which is naturally dependent on the extent of the exposure. Thus
waves about 560 ft. in length have been met with during severe gales in
the Atlantic Ocean; whilst waves from 600 to 1000 ft. long are regarded
as of common occurrence in the Pacific Ocean during storms.

The rate of transmission of the undulation also varies with the
exposure; for the ordinary velocity of the apparent travel of waves in
storms has been found to amount to about 22 m. an hour in the Atlantic
Ocean, and to attain about 27 m. an hour off Cape Horn. The large waves,
however, observed in mid-ocean do not reach the coast, because their
progress is checked, and their height and length reduced, by
encountering the shelving sea-bottom, which diminishes the depth of
water on approaching the shore; and the actual waves which have to be
arrested by breakwaters depend on the exposure of the site, the
existence of continuous deep water close up to the shore, and the depth