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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

These are manuscripts and typescript documents of 34 different princely states that existed as distinct political entities in pre-independence India. Although the majority of these states were tiny principalities in western India (primarily in what is now Rajasthan), some (e.g., Hyderabad) were located in other regions of India and represented major powers in the region at that time.

Letters written to Gay from political and literary contemporaries such as Horace Greeley, Charles Sumner, and William Bryant; reports in letter form from his reporters at the front during the Civil War; and personal correspondence including many letters from his wife, Elizabeth Neall Gay. Letters written to Mrs. Gay from family friends and business associates including many from her husband. Correspondence of other members of the Gay family including Walter Gay, Sarah Gay, and Allan Gay. Diaries, notebooks, and journals of Sydney Howard Gay.