Page:Popular Science Monthly Volume 16.djvu/49

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at one place and slight at another, the air will as naturally flow from the former toward the latter as water will down an inclined plane; and as the velocity of the water will depend on the inclination of the plane, so will the violence of the wind be chiefly due to the difference of pressure: hence the direction and force of the wind are predicted. Again, whether the day will be warm or cold depends mostly on the temperature of this wind; and, furthermore, if it contains much vapor and blows toward a point where the temperature is lower than that from which it started, clouds, or rain, or snow will follow, according to the difference of temperature and the supply of vapor; but if a saturated wind blows toward a place where the temperature is high, and air dry, its moisture will be licked up by the thirsty air, and a mere haze will ensue, or clear weather continue.

This problem in its ever-varying conditions is the one daily solved by the Weather Bureaus of several Governments, in the interest of agriculture, comfort, and commerce; and perhaps nowhere more successfully than by our own. With its large corps of trained observers, its military discipline, variety of standard instruments, extensive field of operations covered by telegraphic lines, liberal Government support, and educated intelligence to guide the whole, there is every reason for the confidence so generally felt in the weather prognostics of the Signal Office of the United States Army.

With this preliminary glance at meteorology on the land, I shall now pass to a consideration of it as regards the ocean—the subject proper of this article; and as I have already divided the problem into three phases, it will be convenient to maintain this distinction—only, that for the ocean, the cases reduce to two: first, to seek out the hidden cause of the winds, whether as the gentle trades that scarcely ruffle the waters over which they glide, or as the violent hurricane that lashes the waves into a tempest of confusion; and, secondly, to determine the many items that, together, make up the climate of small areas of every sea.

The third phase of the problem on land is entirely excluded from the ocean. There we can not establish fixed stations and spread a web of electric wire over them, with some guiding genius ensconced in the midst. We can not (as is done every morning in the United States, England, France, and Germany, for the limits of each country) say what the weather will be, and how the winds will blow, for the ensuing twenty-four hours, in the Indian Ocean, the South Seas, or the North Atlantic. But we can give information yielding in no degree in importance to this purely ephemeral benefit; and the manner in which this is obtained and published is what I shall fully describe hereafter.

To the late Commander M. F. Maury, of the United States Navy, is due the credit of having given to ocean meteorology that vigorous impulse that placed it in the foremost rank of pursuits, and justly