ured
by the construction of one or more "breakwaters." These breakwaters,
having to prevent the waves that beat upon the coast from reaching the
site which they are designed to protect, must be made sufficiently
strong to withstand the shocks of the waves during the worst storms to
which they are exposed. It is therefore essential, before constructing a
breakwater, to investigate most carefully the force, periods and
duration of the winds from the quarters to which the work will be
exposed, the distance of any sheltering land from the site in the most
stormy direction, the slope of the beach and the depth of the sea in the
neighbourhood of the shore, and the protection, if any, afforded by
outlying shoals or sandbanks. In a tidal sea, the height required for a
breakwater is affected by the amount of tidal range; and the extent of
breakwater exposed to breaking waves depends upon the difference in
level between low and high water. The existence, also, of any drift of
sand or shingle along the shore must be ascertained, and its extent; for
the projection of a solid breakwater out from the shore is certain to
affect this littoral drift, which, if large in amount, may necessitate
important modifications in the design for the harbour.

Winds.

Observations of the force and prevalence of the winds from the different
quarters at the various periods of the year, and the instruments by
which they are recorded, belong to the science of meteorology; but such
records are very valuable to the maritime engineer in indicating from
which directions, open to the sea, the worst storms, and, consequently,
the greatest waves, may be expected, and against which the most
efficient shelter has to be provided. Moreover, it is necessary, for
constructing or repairing a breakwater, to know the period of the year
when the calmest weather may be safely anticipated, and also the stormy
season during which no work should be attempted, and in preparation for
which unfinished works have to be guarded by protective measures. In the
parts of the world subject to periodical winds, such as the monsoons,
the direction and force of the winds vary with remarkable regularity
according to the seasons; and even such uncertain occurrences as
hurricanes and cyclones generally visit the regions in their track at
definite periods of the year, according to the locality. Even in western
Europe, where the winds are extremely variable, violent gales are much
more