Mendelsohn, Charles Jastrow

8 Dec. 1880–27 Sept. 1939

Charles Jastrow Mendelsohn, cryptographer, was born in Wilmington, the son of Rabbi Samuel and Esther Jastrow Mendelsohn. He was graduated from the Episcopal Academy, Philadelphia, Pa., in 1896 and received an A.B. degree in 1900 and a Ph.D. degree in 1904 from the University of Pennsylvania, where he was a Harrison Scholar and a member of Phi Beta Kappa. Joining the faculty of the College of the City of New York as a tutor in Greek in 1905, he became an instructor in 1907. On leave from his teaching position during World War I, he served in the censorship division (foreign language, postal, and newspaper censorship) of the Post Office Department in 1917. In 1918–19 he was a captain in the Military Intelligence Division of the War Department General Staff. Here he worked on the solution of codes used by the German Foreign Office.

Returning to City College in 1920, he never abandoned his interest in cryptography. He prepared a number of papers on code-word structure, the theory and construction of cable codes, and allied subjects, particularly the mathematics of code-word structure. His continued research on codes led to the preparation of studies in diplomatic codes for the U.S. government.

Mendelsohn also became interested in the history of cryptography and began collecting books on the subject. At the time of his death, he owned what has been described as "probably the most important cryptographic library in America, if not in the world." This collection was bequeathed to the University of Pennsylvania. Shortly before his death he completed what is considered to have been his most important work, "The Earliest Solution of a Multiple Alphabet Cipher Written with a Key," published in 1939 in the Signal Corps Bulletin. He was also the author of Studies in the Word-Play in Plautus . . . : I. The Name-Play and II. The Use of Single Words in a Double Meaning (1907), the first portion being his doctoral dissertation, and the coauthor of The Zimmerman Telegram of January 16, 1917, and Its Cryptographic Background. He contributed to many scholarly journals including the Proceedings of the American Philosophical Society and Scripta Mathematica, as well as to government publications.

In the fall of 1939, in connection with the war in Europe, Mendelsohn was recalled to active duty, but in the midst of preparations to leave New York he became ill and died of meningitis. Burial followed in the Hebrew Cemetery at Oakdale Cemetery, Wilmington. Never married, he was survived by his mother.