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Page:Popular Science Monthly Volume 34.djvu/859

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SKETCH OF JAMES P. ESPY.

a distinguished professor, that I had failed to convince men. of science of the truth of my theory, and that I had appealed to the people, who are incapable of judging. It became, therefore, necessary to obtain authority against authority."

The origin of the studies upon which the theory of storms is based is traced in the opening paragraph of the "Philosophy" to the result described by Dalton, that the quantity of vapor in weight, existing at any time in a given place, could be determined by means of a thermometer and a tumbler of water cold enough to condense on its outside a portion of the vapor in the air. "It occurred to me at once," Prof. Espy says, "that this was the lever with which the meteorologist was to move the world. I immediately commenced the study and examination of atmospheric phenomena, determined to discover, if possible, what connection there is between rain and the quantity of vapor in the atmosphere." Prof. Espy prefaced his paper in the British Association by saying that he had found, by examining simultaneous observations in the middle of storms and all round their borders, that the wind blows inward on all sides of a storm toward its central parts; toward a point if the storm is round, and toward a line if the storm is oblong, extending through its longest diameter. The theory is, in brief, that every atmospheric disturbance begins with the ascension of air that has been rarefied by heat. The rising mass dilates, and, as its temperature falls, precipitates vapor in the form of clouds. Owing to the liberation of the latent heat, the dilatation continues with the rising till the moisture of the air forming the upward current is practically exhausted. The heavier air flows in beneath, and, finding a diminished pressure above it, rushes upward with constantly increasing violence. The great quantity of aqueous vapor precipitated during this atmospheric disturbance gives rise to heavy rains. Much of this theory still holds good; but it has been found that the motion of the wind in storms is rotary.

Besides his explanation and proofs of this theory. Prof. Espy presented to the British Association a paper on "Four Fluctuations of the Barometer." The theory was more fully elaborated in "The Philosophy of Storms," which was published in a large octavo volume by Little, Brown & Co., Boston, in 1841, and was re-enforced by detailed descriptions of a large number of storms occurring on the land and the ocean, the course of which the author had been able to follow and study with considerable accuracy. It also contained his answers to the citicisms which had been made against his theory in the British Association and elsewhere by prominent men of science and rival meteorologists. In it, furthermore, he defended his theory that storms could be produced by large fires making local disturb-