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1 12
HARBOUR ENGINEERING.
aggravated by physical and molecular changes, resulting in deterioration in
strength and durability. The intensity of the external forces which make
for disruption is enormous, exceeding beyond all comparison the power of the
wind on land structures. Wave agency is a thousandfold more potent than
the most intense atmospheric movement. There are, moreover, insidious
denizens of the sea, infesting it by millions, which, by their concerted action,
Fie. 92. —Section of Portland Breakwater.
are capable of undermining the hårdest and soundest building materials, and
that in the most secret and surreptitious manner, the damage being as un-
suspected as it is irrémédiable.
Such inimical natural phenomena constitute the normal and characteristic
environment of all maritime structures. They are bonded together, as it
were, in an offensive alliance to urge incessant and unrelenting war upon
mau’s handiwork—sapping, wearing, battering, making subtle inroads and
open breaches, working now by patient effort, long sustained, and now by
sudden, prodigious feats, month after month, year in and year out, knowing
neither truce nor armistice.
The Sea Wave.—But by far the mightiest of the forces arrayed against
the harbour barrier is the sea wave. This mysterious product of wind and water
is endowed with tremendous disruptive power. It acts with all the magnipotent
impulse of a huge battering ram, while, at the same time, it is equipped with
the point of the pick and the edge of the wedge. It is, in fact, one of the
most complex, the most volatile, the most pertinacious, and the most incom-
préhensible of natural forces.
From an engineering point of view, we have little to do with abstract
theories of wave formation. Mathematically, the subject is too abstruse for
any but very accomplished and capable mathematicians, and the intricacies
of calculation are interesting only as academical exercises. Many of the
theories advanced are merely tentative and lack substantial corroboration •
others, while generally accepted, are still the subjects of spéculation and
inquiry. Thus, no useful purpose would be served by pursuing an investiga-
tion into the laws and phenomena of water undulation. Students who
wish to do so, however, may consult the articles on Wave and Tide in the