ESPY, James Pollard, meteorologist, born in Westmoreland County, Pennsylvania, 9 May 1785; died in Cincinnati, Ohio, 24 January 1860. He was graduated at Transylvania University in 1808, and in the same year became principal of the classical academy in Cumberland. Afterward he studied law, was admitted to the bar, and practiced for four years in Xenia, Ohio. In 1817 he accepted a call to the classical department of the Franklin institute, and while in Philadelphia published in the "Journal of the Franklin Institute" his earliest researches in meteorology. After some years of investigation he advanced the theory that every great atmospheric disturbance begins with the uprising" of air which 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 dilation 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. The physical principles on which this theory was based were correct, and it is so far supported by observation. It found many adherents, and attracted the attention of scientists abroad.

In 1840 he visited Europe, and presented his views before the British association, to whose transactions he contributed papers on "Storms" and on the "Four Fluctuations of the Barometer." A committee of the French academy of sciences examined his theory, and reported favorably on it. During the debate that took place in the academy, Arago said, "France has its Cuvier, England its Newton, America its Espy." However, subsequent researches led to important modifications of his views by the so-called rotary theory that is now generally accepted. Mr. Espy believed that rains could be produced artificially by means of fires sustained long enough to produce a powerful upward current, which would initiate the action as previously described. He petitioned congress and the legislature of Pennsylvania for an appropriation to enable him to perform the experiment, but without success.

In 1843 he received an appointment under the war department, enabling him to prosecute his investigations in the Washington observatory, and several volumes of his reports were published. While holding this office he instituted a service of daily bulletins, in conjunction with the newspapers and the telegraph companies, on the condition of the weather in different localities. This constituted the earliest efforts of the weather bureau, which has since developed into an important branch of the war department. Mr. Espy was a member of the American philosophical society, received its Magellan gold medal in 1836, and in 1841 was elected a corresponding member of the Smithsonian institution. He was sometimes called the " Storm King." He published " Philosophy of Storms" (Boston and London, 1841).