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Professional and personal files including Armstrong's correspondence with professional associations, other engineers, and friends, his research notes, circuit diagrams, lectures, articles, legal papers, and other related materials. Of his many inventions and developments, the most important are: 1) the regenerative or feedback circuit, 1912, the first amplified radio reception, 2) the superheterodyne circuit, 1918, the basis of modern radio and radar, 3) superregeneration, 1922, a very simple, high-power receiver now used in emergency mobile service, and 4) frequency modulation - FM, 1933, static-free radio reception of high fidelity. More than half the files concern his many lawsuits, primarily with Radio Corporation of America, over infringement of the Armstrong patents. Litigation continued until 1967. Other files deal with his work in the Marcellus Hartley Research Laboratory at Columbia University, 1913-1935, and with the American Expeditionary Forces in France during World War I, his Air Force contracts for communications development, Army research during World War II, the Radio Club of America, the Institute of Radio Engineers, FM development at his radio station at Alpine, N.J., the use of FM in television, his involvement in Federal Communications Commission hearings and legislation, and his work with the Zenith Radio Corporation. Also, letters to H.J. Round

Correspondence relating to Erskine's various educational, musical and literary interests; manuscripts of his writings; lecture notes for college courses; souvenirs of his army service in World War I and his Columbia University professorship, and student papers from his own school and college days. Also, biographical file, scrapbooks, and articles.

Correspondence, manuscripts of poems, and manuscripts of lectures by Benjamin. The correspondence consists of original letters of Benjamin, typescript and photostatic copies of Benjamin letters in other libraries, and letters to Benjamin from some of his literary contemporaries including Paul Hamilton Hayne, Willis Gaylord Clark, John Lothrop Motley, and Fitz-Greene Halleck. Many of the letters relate to Park Benjamin's lecture tours. There are other family letters and many documents relating to the Benjamin family,and two letterbooks of John Lothrop Motley. Also, a large amount of genealogical material of the Benjamin family, and its related families from the 16th century to the present day. There are also financial records, monographs, clippings, and photographs.

This collection is primarily concerned with Prof. James Renwick and his professional correspondence and papers, both as Professor of Natural Philosophy (Physics) at Columbia College and as a leading engineer. Many certificates of membership in honorary societies are included. There are letters from Washington Irving (1783-1859) to Prof. Renwick and to his mother, Jane Jeffrey Renwick, pertaining to contemporary events and Irving's own activities. The letters to Mrs. Renwick are about the travels and experiences of Irving and Renwick abroad. The collection also covers the affairs of the Prof. Renwick's grandfather, including documents concerning his land grants in New York State, and those of James Armstrong Renwick, including his valedictory address at Columbia College in 1876 and his class reunion in 1916. There are many legal documents, letters, and manuscripts of various members of the Renwick and Brevoort families; among these are Prof. Renwick's notes on his family genealogy and a memoir of Jane Jeffrey Renwick. Correspondents include Clement Clarke Moore, John A. Dix, Martin Van Buren, Secretary of State John Forsyth, and Secretary of the Navy James K. Paulding. There is one letter from Sir Edward Sabine (1788-1883), President of the Royal Society, giving his views on the American Civil War.