Erastus Lyman De Forest was born on June 27, 1834 in Watertown, Connecticut, United States. He descended from an old Walloon family, and was the only son of Dr. John and Lucy Starr (Lyman) De Forest, and the last of the male line of Benjamin De Forest of Watertown, Connecticut, United States.
Entering Yale at the age of sixteen, he was graduated in 1854 with the degree of Bachelor of Arts. He then pursued his scholastic work in the engineering department of the Sheffield Scientific School (Yale), where he was graduated two years later with the degree of Bachelor of Philosophy. In 1867 he received the degree of Master of Arts.
Although DeForest inherited sufficient means from his grandfather to provide for his modest needs, he determined to show his independence of such assistance. The gold fever of 1849 had not yet subsided when he left Sheffield, and a year later he went to California where for a time he worked in the mines. Inspired no doubt by the love of travel, he next went to Australia and became a tutor in the University of Melbourne. After this venture he traveled in the East and in Europe, finally returning to America to the enjoyment of a more quiet life, devoting the rest of his years to mathematical research in a field at that time but little cultivated in the United States.
In 1886 he gave $4, 000 to Yale to increase the fund established by his father in 1855—still the source of the De Forest Mathematical Prizes.
Just before his death (1888) he gave $10, 000 toward the endowment of a chair of mathematics in that university. His scientific work related chiefly to the theory of probability and errors and has come to be looked upon in late years as showing unusual ability. His first paper appeared in the American Journal of Science in 1866, and from that time until his death he published on an average approximately a paper a year, all in the same general field. Most of these papers appeared in the journal mentioned, in The Analyst, or in the Smithsonian Reports. Being of a technical nature, they failed to attract popular attention and, indeed, were hardly appreciated during his lifetime by scientists in his particular line of interest.
Hugh H. Wolfenden, however, called the attention of a mathematical congress at Toronto, in 1924, to the notable work done by De Forest. In the paper there presented it was shown that his contribution to the development of formulas for graduation by linear compounding (a subject of great importance in actuarial work), “in a most invaluable series of papers which appeared in the Smithsonian Reports of 1871 and 1873, a pamphlet, Interpolation and Adjustment of Series (1876), and The Analyst (Des Moines), 1877-80, ” was one of the most important of its kind ever made by an American scholar.
DeForest never married.
