' STRONG, TITEODORE, LL.D., 1790-1869; b. Mass. ; graduated at Yale in 1812, taking the mathematical prize; tutor in mathematics at Hamilton college, 1812-16; professor of mathematics at Hamilton, 1816-27. A new geometrical demonstration by him of the values of sines and co-sines of the sum and difference of two arcs, and a so lution of a difficult pjob]em in diophantine analysis, were published in the American Journal of Science in 1818. Other important papers appeared in subsequent numbers.
After having mastered the Principia of Newton and the subjects added by its com mentators, he addressed himself to the study of the more modern analysig of La Grange and Laplace. This required a knowledge of the French language which he did not possess, but he soon taught himself sufficient to be able to read mathematical works in French as well as in English or Latin. In 1827, upon a second invitation from Rutgers college, N. J., he became professor of mathematics and natural philosophy in that in stitution, and removed to New Brunswick, where he remained during the rest of his life, performing the duties of his chair till 1862. Prof. Strong made many important contributions to mathematical science, among which may be mentioned the solution of what is known as the irreducible case of cubic equations of Cardan, a result which had long been sought in vain. He also devised a method for the application of the bi nomial theorem for the extraction of the roots of whole numbers. His two principal systematic works are: A Treatise on Elementary and Higher Algebra (1859); and A Treatise on the Differential and Integral Calculus (1869). Both of these treatises contain much original work. In the Algebra, besides what is mentioned above, there is: 1. A direct investigation of the binomial theorem; 2. A simple method of finding integral algebraic roots; 3. A method of solving quadratic equations without completing the square. 4. The doctrine of continued fractions deduced immediately from the form of the quotients and remainders iu common division. 5. A new demonstration of the method used for finding the limits of the real roots of equations, including the theorem of Descartes. 6. A new and much more simple method than that of Sturm for finding the first figures of the real roots of an equation. The work on Calculus, written in his 7,8th year, and without the aid of notes or books, has many original features, and is di vested of technicalities and formulas which have become the accretions of time. It
contains a solution, by a new and beautiful method, of the problem, " To find the area bounded by the ordinate of a plane curve drawn through the origin of the co-ordinates by any other ordinate and the intercepted parts of the axis and the curve, supposing the ordinates to be constantly positive between the preceding limits." Prof. Strong was a contributor to various mathematical and scientific journals for the greater part of his life. To the American Journal of Science he contributed 22 papers between 1818 and 1845. To the Mathematical Diary, published at New York and edited at first by Dr. Robert Adrian and afterward by James Ryan, he also contributed. To the Mathematical Miscellany, edited by Mr. Charles Gill at Flushing, L. I., he contributed 22 papers; to the Cambridge _Miscellany, edited by profs. Peirce and Lovering, seven papers; and to the Mathematical Monthly, edited by I. D. Runkle, two papers. He also communicated five different papers to the National academy of sciences from 1864 to 1867 inclusive. Among the papers contributed to the American Journal of Science arc a systematic dis cussion of the laws regulating the action of a central force, the path of the curve pro-1 duced thereby, and the mutual action of a system of bodies; a discussion of the par allelogram of forces, their composition and resolution, and the statical equilibrium. In volume xvi. of the journal, on p. 286, there is a deduction of the differential equation which constitutes the fundamental formula for expressing the angular velocity of a planet in terms of its radius vector, and thence, the force being given, the law of the curve of revolution, and of all curves produced by a central force, corresponding to the result given by Laplace in the first part of his second book of the Michanique Celeste, and to that of Newton in the 41st proposition, section viii., of the Principia. He was one of the original members of the National academy of science, and was also a member of the Connecticut academy of arts and sciences at New Haven, of the American academy of arts and sciences at Boston, and of the American philosophical society at Philadelphia.