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REGULAR AND IRREGULAR UNDULATIONS. 59
CHAPTER VI.
WAVES OF THE SEA. REGULAR AND IRREGULAR UNDULATIONS.—HEIGHT OF
THE WAVES.—THEIR SIZE AND SPEED.—GROUND-SWELL. COAST-WAVES.
The sea rarely presents a glassy surface. When the atmosphere is
calm, which however is commonly the case before a tempest, the water'
is sometimes so very smooth that every object is reflected by it with a
perfectly sharp outline; the only changes which seem to affect the vast
motionless sheet of water are those produced by the mirage, which
makes the distant horizon glitter like a long band of silver or steel; the
fishermen then say that " the sea is reflecting itself." But this tranquillity of the water is a very uncommon phenomenon, except in the Mediterranean and other seas, where there is only a slight tide. Usually the
wind, either in breezes or tempests, now aiding and now retarding the
ebb and flow, raises the sea into waves, more or less high, which sometimes roll onward regularly, or are dashed against and cross one another.
Even during calms, the waves, still obeying the impulse of recent winds,
continue to roll across the ocean in long undulations. One of the grandest spectacles at sea is offered by these regular movements of the waves
in perfectly calm weather, when not a breath stirs the sails; high, blue,
and foamless, the liquid masses succeed one another at intervals of 200
to 300 yards, pass under the ship in silence, and, pursued by other waves,
are lost in the far distance. One contemplates with a feeling of admiration, not unmixed with terror, the calm and majestic wave advancing
like a moving rampart, as if about to swallow up all before it, and yet
hardly leaving a sign to mark its passage. These waves appear with
surprising regularity during the autumnal calms, under the Tropic of
Cancer, and almost at every season in the narrower part of the Caribbean Sea toward the Gulf of Darien ; there the waves are seen silently
to advance, and slightly raise the ship, passing onward with scarcely a
murmur, as regularly as the furrows of a field, and stretching as far as
the eye can see.
Such perfectly regular waves as these can only be formed in seas exposed to the influence of equable winds, such as the trade-winds. Wherever the winds are uncertain and shifty, blowing in gusts, it is evident
that the waves driven by them can not assume a regular form or follow
in a uniform direction. For aerial currents constantly vary in their
speed; being composed of strata of unequal force, which, moving at a
rate different from that of the surface of the sea, alternately increase and
diminish in force. Under the influence of these variable atmospheric impulses, the waves must necessarily vary in height and speed, and their
| Title | The ocean, atmosphere, and life |
| Creator | Reclus, Elisée |
| Publisher | Harper |
| Place of Publication | New York |
| Date | 1873 |
| Language | eng |
| Type | Books/Pamphlets |
| Title | 00000068 |
| Type | Books/Pamphlets |
| Transcript | REGULAR AND IRREGULAR UNDULATIONS. 59 CHAPTER VI. WAVES OF THE SEA. REGULAR AND IRREGULAR UNDULATIONS.—HEIGHT OF THE WAVES.—THEIR SIZE AND SPEED.—GROUND-SWELL. COAST-WAVES. The sea rarely presents a glassy surface. When the atmosphere is calm, which however is commonly the case before a tempest, the water' is sometimes so very smooth that every object is reflected by it with a perfectly sharp outline; the only changes which seem to affect the vast motionless sheet of water are those produced by the mirage, which makes the distant horizon glitter like a long band of silver or steel; the fishermen then say that " the sea is reflecting itself." But this tranquillity of the water is a very uncommon phenomenon, except in the Mediterranean and other seas, where there is only a slight tide. Usually the wind, either in breezes or tempests, now aiding and now retarding the ebb and flow, raises the sea into waves, more or less high, which sometimes roll onward regularly, or are dashed against and cross one another. Even during calms, the waves, still obeying the impulse of recent winds, continue to roll across the ocean in long undulations. One of the grandest spectacles at sea is offered by these regular movements of the waves in perfectly calm weather, when not a breath stirs the sails; high, blue, and foamless, the liquid masses succeed one another at intervals of 200 to 300 yards, pass under the ship in silence, and, pursued by other waves, are lost in the far distance. One contemplates with a feeling of admiration, not unmixed with terror, the calm and majestic wave advancing like a moving rampart, as if about to swallow up all before it, and yet hardly leaving a sign to mark its passage. These waves appear with surprising regularity during the autumnal calms, under the Tropic of Cancer, and almost at every season in the narrower part of the Caribbean Sea toward the Gulf of Darien ; there the waves are seen silently to advance, and slightly raise the ship, passing onward with scarcely a murmur, as regularly as the furrows of a field, and stretching as far as the eye can see. Such perfectly regular waves as these can only be formed in seas exposed to the influence of equable winds, such as the trade-winds. Wherever the winds are uncertain and shifty, blowing in gusts, it is evident that the waves driven by them can not assume a regular form or follow in a uniform direction. For aerial currents constantly vary in their speed; being composed of strata of unequal force, which, moving at a rate different from that of the surface of the sea, alternately increase and diminish in force. Under the influence of these variable atmospheric impulses, the waves must necessarily vary in height and speed, and their |
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