Espy, James Pollard

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Espy, James Pollard

(b. Washington Country, Pennsylvania, 9 May 1785; d. Cincinnati, Ohio, 24 January 1860)


Espy was educated at Transylvania University in Lexington, Kentucky, and taught school before embarking upon a full-time career as a meteorologist in the mid-1830’s. He did his earliest known work in the field in 1825 while teaching at the Franklin Institute in Philadelphia, his interest stemming from the writings of Dalton and Daniell.

The most common kind of meteorological activity in the antebellum United States was the gathering of observations. From these observations, physical explanations were sometimes deduced (e.g., William Redfield) or the data were analyzed mathematically in some fashion (e.g., Elias Loomis). From such roots arose movements to develop networks of observers and regular systems for processing the resulting data. Espy participated in this tradition in the founding of a system of meteorological observations in Pennsylvania in 1836 and in his labors (ca. 1840–1852) to erect a national system of volunteer weather observers which was supplanted by Joseph Henry’s telegraph-linked corps of observers.

Espy’s principal significance in the history of meteorology arises from a less typical kind of research for his time and place. By direct experimentation, he tried to derive physical concepts supported by quantitative data. Others might talk of the role of atmospheric electricity; Espy flew giant kites.

Espy’s most notable experimental work centered on heat effects. He devised an instrument, the “nephelescope,” to simulate, as it were, the behavior of clouds and, particularly, to measure the dry and moist adiabatic cooling rates. While the resulting data varied from the correct values, Espy displayed great physical insight in deducing the role of latent heat in cloud formation and rainfall. He was, apparently, the first to point out that the latent heat released by condensation of the vapor in clouds resulted in a considereable expansion of the air, the latent heat, therefore, providing the energy for continued rain and upward movement of the cloud.

As the concept of the saturated adiabatic expansion of rising air currents is basic to meteorology, Espy clearly merits recognition as an important pioneer. Lacking any sophisticated mathematical apparatus or a knowledge of modern thermodynamics and other factors involved in cloud dynamics, Espy’s work did not lead directly to the work of Kelvin and others from which the modern theory stems.

It is possible, however, that his enthusiastic proselytizing for his views helped pave the way for the acceptance of the later work. In 1840 Espy addressed the Glasgow meeting of the British Association for the Advancement of Science. An account of his theories sent to the French Academy was favorably reviewed in the Competes rends in 1841 by a committee whose members were D. F. J. Arago, C. G. M. Pouillet, and J. Babinet. Espy lectured widely in the United States, undoubtedly deserving credit for stirring up popular interest and support for meteorology.

Working against recognition of his theories, however, especially their very real contributions, was this same quality of enthusiastic commitment. Espy was most contentious and not always receptive to criticism. Time would prove W. C. Redfield, with whom Espy was involved in a controversy, correct on the motion of storms; from his results Espy deduced spectacular conclusions, some unconvincing or apparently refutable. (His suggested burning of forests to produce rainfall was disregarded by narrow minds immune to the need for controlled experiments.)

In short, because of his aprofessional behavior the emerging community of professional scientists was inclined to overlook his real contributions, which have been rediscovered periodically by historically inclined meteorologists.


I. Original Works. A satisfactory list of Espy’s articles is in the Royal Society Catalogue of Scientific Papers, II, 522–523. For the full flavor of the man and his ideas, it is necessary to consult his monographic works. The best known is The Philosophy of Storms (Boston, 1841). Less known but also quite valuable is Report on Meteorology, 4 vols. (Washington, D.C., 1843–1857), submitted by Espy in his anomalous role as the national meteorologist.

Friends of his succeeded in attaching riders to bills authorizing funds for Espy’s work. None of the executive establishments requested this work, and as a result these reports were issued separately under rather odd circumstances. The first (1843) is a report to the surgeon general of the army and is fairly rare. The second (1850) and third (1851) are reports to the secretary of the navy. Both are nos. 559 and 560 of the congressional series (Senate executive document no. 30, 31st Congress, 1st session); their being bound together produces problems in determining the dates of the two reports. The fourth and last report was simply submitted by the president to Congress in 1857, but most of the work is of an earlier date. It too is in the congressional series (no. 889) as Senate executive document no. 65, 34th Congress, 3rd session. (For a modern comment on the four Reports, see Meteorological Abstracts [February 1955], p. 143.)

MS sources for Espy may be found in the archives of the American Philosophical Society and the Franklin Institute, both in Philadelphia. There is much on Espy’s activities in the papers of his two leading American contemporaries in meteorology, Elias Loomis and W. C. Redfield, in the Beinecke Library, Yale University, New Haven. The personal papers of Joseph Henry and the archives of the Smithsonian Institution in Washington, D.C., during Henry’s secretariat have documents relating to Espy and on the development of American work in meteorology.

II. Secondary Literature. The earliest authoritative statement on Espy is the report in the Comptes rendus hebdomadaires de l’Académie des sciences, 12 (1841), 454–465, referred to above. After Espy’s death, Alexander Dallas Bache, an old friend, wrote a necrology which can stand as a good summary of how Espy was regarded by the professional scientists. It appears in the Smithsonian Institution Annual Report for 1859 (Washington, 1860), pp. 108–111. In 1894 William Morris Davis, a fine geographer and geologist, presented a rather superficial view of Espy’s period in American meteorological work in “The Redfield and Espy Period,” a paper presented at the International Meteorological Congress, Chicago, 21–24 August 1894 (U.S. Weather Bureau, Bulletin no. 11, pp. 305–316).

Espy is briefly referred to in W. J. Humphreys, “A Review of Papers on Meteorology and Climatology Published by the American Philosophical Society Prior to the Twentieth Century”, in Proceedings of the American Philosophical Society, 86 (Sept. 1942), 29–33.

Part of the modest revival of interest in Espy in recent years is undoubtedly the result of his appearance in K. Schneider-Carius, Wetterkunde Wetterforschung, Geschichte ihrere Probleme und Erkenntnisse in Dokumenten aus drei Jahrtausenden (Munich, 1956), pp. 192–196. Espy is discussed and some of his unpublished documents are printed in Nathan Reingold, Science in Nineteenth Century America: A Documentary History (New York, 1964), pp. 92–107, 128–134.

J.E. McDonald, “James Espy and the Beginnings of Cloud Thermodynamics,” in Bulletin of the American Meteorological Society, 44 (1963), 633–641, is an important recent appraisal. W. E. Knowles Middleton, A History of the Theories of Rain and Other Forms of Precipitation (London, 1965), pp. 155–160, is the most recent retrospective appraisal of Espy.

Nathan Reingold

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