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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

Manuscript account books and documents which illustrate and document the history of accounting and business procedures from the 14th century into the 20th century. The earliest item is Ms. 18, a Papal bull relating to notaries and appointing Julius de Gentilibus as a notary; the latest is an invoice book from 1941. The types of volumes contained in this collection include instruction books, daybooks, waste books, journals, bank books, ledgers, receipt books, storage books, invoice books, registers, ships' logs, letter books, diaries, town books, tax roll books, articles of agreement, bills of sale, deeds, wills, and many other significant items. The material originated in many countries around the globe, and represents a range of business and occupations from household to trading company (e.g., English (East India Company) and French East Indian Company (Compagnie des Indes orientales) volumes), and from itinerant laborer to lawyer and physician. The majority of the manuscripts are English and American of the 17th, 18th, and 19th centuries. The earliest American account is Ms. 75, 1690-1730, Josiah Winslow, Plymouth, Mass.