O, thou art fierce and wild!
Thy mighty chariot through the black skies lashing,
The cloud-shapes round the mountain-summits dashing,
The waves of ocean round the wrecked bark crashing—
O, thou art fierce and wild!”
EN find no difficulty in recognizing law and system in the phenomena that are of constant or frequent recurrence. That which is most difficult to explain, may pass without a serious thought so long as it manifests no stupendous or sudden power. The water may wear away the stone for centuries and its progress be unheeded by those who daily visit the pool.
So all observe and admire the beauty and order that prevails in the system of winds hitherto described. Their movements seem so simple and natural, that people take them as a matter of course. Rather, we should say, they may be depended upon with such certainty that the laws which they followed were unheeded for more than six thousand years. Relying on result, men gave themselves no concern about principle.
But in the sudden storm, the cyclone or tempest that comes sweeping the land with hardly any warning, flooding and destroying, men find mystery.
And who is not justly awed thereby? What other power so easily and frequently wrecks and ravages? Who may point out its course or stay its progress?
And indeed it would seem difficult at first to find any law or system that controls the motion of the storm. If a rain storm always came from the same direction; if unusually high winds always blew from the same quarters, just as the moderate breezes of spring and summer can always be expected from the same general direction, it would appear that there was much greater subordination to definite law. But what can be more perplexing than to have a storm blow violently from one quarter for a time, and after a brief calm to blow with equal violence the other way? Can such phenomena be explained by any principles hitherto discovered?
What is a storm? Strictly speaking, it is any marked or unusual disturbance of the normal atmospheric conditions. There may be excessive wind: there may be cessation of the customary winds. Two great classes are found: cyclonic, or low area storms, and anti-cyclonic, or high area storms. The former may be accompanied by heavy rainfall or snow; the latter is usually noted for absence of either. It is with the low area storm that we must deal at present.
This term is used to designate all storms which are marked by low barometer, and therefore it is clear that such are accompanied and partially occasioned by an unusual amount of moisture in the atmosphere. The resultant commotion is usually extensive, the storm centre traveling across the country; but occasionally the effects are perceptible only for a short distance, the storm centre either breaking up or ascending to the upper atmosphere.
By a cyclonic storm is signified a storm characterized by unusually low barometer, and a wind system blowing spirally inward, as in a genuine cyclone. They usually affect only the lower strata of the air. Quite frequently they are broken up by striking low mountain ranges, such as the Alleghany system: and often pass Mount Washington without making their presence felt at the signal station on its summit. To what extent they are influenced by or are due to the upper air currents is therefore unknown, though not a few of the attendant phenomena indicate that the latter are of no little importance.