HAYDEN, Horace H., dentist, born in Windsor, Connecticut, 13 October, 1769; died in Baltimore, Maryland, 26 January, 1844. His parents were impoverished by the war of the Revolution, in which his father was an officer. The son taught school at sixteen years of age, studied architecture, and practised that profession until his majority. He then was brought in contact with Dr. Greenwood, the dentist, of Washington, in New York. He studied dentistry, and settled in 1804 in Baltimore, where he practised with eminent success till his death. Dr. Hayden stud= fed medicine, and geology also, and was called in consultation by the chief physicians of Baltimore. His correspondence in Europe on geology, botany. and dental science was extensive. Dr. Hayden was a surgeon of Maryland troops in the battle of North Point in 1814. He received the honorary degree of M. D. from Jefferson college in 1837, and from Maryland medical university in 1840. He was the founder and incorporator, and first president, of Baltimore college of dental surgery, and its first professor of dental pathology and physiology from 1839 till his death. He was also founder and president until his death of the American society of dental surgery, and a founder and vice president of the Maryland academy of science and literature. He was a member of many other learned societies, and published "Geological Essays, or an Inquiry into Geological Phenomena to be found in Various Parts of America" (Baltimore, 1820), which Benjamin Silliman said "should be a text book in all our schools," and papers, including "New Method of preserving Anatomical Preparations," in the "American Medical Record" of 1822; "Notice of a Singular Ore of Cobalt and Manganese," in "Silliman's Journal" (1822); "The Bare Hills near Baltimore," in "Silliman's Journal" for 1832; and "Silk Cocoons," in the "Journal of the American Silk Company" (1839).