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 552 in which the writer assisted him, is not remembered, but Mather declared that he was satisfied with it. Such was his occupation on one of the coldest days in winter, during the whole of the Saturday afternoon allowed to the corps for recreation."

On graduating he was assigned to the Seventh Infantry with the customary rank of second lieutenant. He remained at West Point as acting assistant instructor of artillery during the summer encampment of 1828, and was then ordered to the School of Practice at Jefferson Barracks, where he remained until April, 1829. From April to the end of June he was on frontier duty at Fort Jessup, La. He was then detailed to serve as acting assistant Professor of Chemistry, Mineralogy, and Geology in the Military Academy, which duty he performed until the summer of 1835. The assistant professors at the academy at that time were usually detailed from recent graduates, and their terms of service rarely exceeded two years. The fact that Lieutenant Mather was retained in that capacity for six years indicates that he was an unusually successful instructor. During the recess of his course of instruction in 1833 he acted as Professor of Geology, with the permission of the War Department, at Wesleyan University, Middletown, Conn., and the following year received the honorary degree of A. M. from this university. In the summer of 1834 he made a geological survey of Windham County, Conn.

Within the first year after his graduation Lieutenant Mather published in the American Journal of Science a paper entitled On the Nonconducting Power of Water with Regard to Heat. While serving as assistant professor at the academy he contributed other papers to the same journal, and wrote a small textbook. Elements of Geology, which was afterward enlarged and passed through several editions. He wrote also an account of the diluvium for the use of the cadets in their study of geology.

On being relieved from duty at the academy he was assigned to topographical service as an assistant to G. W. Featherstonhaugh in a geological examination of the country from Green Bay to Coteau des Prairies. This work occupied him during the latter half of 1835. He made a topographical map of the St. Peter's (Minnesota) River Valley and a report, which his later associate Whittlesey says he refused to present to the "pretentious English geologist in charge of the expedition," but transmitted direct to the United States Government. When this survey was completed he was promoted to a first lieutenancy and sent to join his regiment on frontier duty at Fort Gibson, in Idaho Territory. The following summer he marched into the Choctaw country in command of his company. Feeling that he could now safely adopt the pursuit of science as a profession, he resigned his commission in the army at the end of August, 1836.