RITTENHOUSE, David, American as tronomer and mathematician: b. Germantown, Pa., 2 April 1732; d. Philadelphia, 26 June 1796. His great-grandfather, Willem Rittinghnysen, a Mennonite from Holland, in 1688 set up, on Wissahickon Creek, the first paper mill in America. From an uncle the boy inherited some books on calculation and geometry, and henceforth his life was determined. Mathe matics and computation became his absorbing passion. He had great facility in mechanical invention and execution. In his 'teens he began to make clocks of wood and metal, and his father set him up in the business of maker of mathematical instruments and clodcs. He is said to have independently discovered the method of fluxion or the calculus when but 19, and to have foreseen its vast utility, before he heard of the claims of Leibnitz and New ton.
In 1763 he laid out the 12-mile radius around Newcastle, which forms the boundary between Pennsylvania and Delaware, accurately with instruments of his own construction, and Mason and Dixon accepted his results as final. In 1769 he located the point where the 41st parallel of latitude, the boundary between Pennsylvania and New York, strikes the Delaware River. The same year the Pennsylvania legislature ap propriated f.200 toward the observations of the transit of Venus. Rittenhouse built an observa tory near his home in Norriton, and in com pany with a committee appointed by the Ameri can Philosophical Society made preparations for the occasion. His results were the best ob tained and the computed parallax of the sun the most accurate then known.
Rittenhouse invented the plan of placing spider lines in the focus of the telescope, an arrangement that has done more to make ac curate measurements possible than almost any thing else. In 1770 he completed his famous orrery based on computations of his own. This showed the movements of the planets and moons in elliptic orbits around their primaries, the phenomena of eclipses and the relative places of the members of the solar system over a tithe of 5,000 years preceding or following.
For this he received f300 from Princeton Uni versity, and a like sum from the legislature of Pennsylvania for a second orrery for the Uni versity of Pennsylvania. The first was injured by the British troops in the Revolutionary War.
Then followed computations of the orbits of comets, surveys of the land between the Delaware and Susquehanna for canal purposes, calculations for almanacs and surveys for a series, of dams to make the Schuylkill River navigable. He was engineer and finally presi dent of the committee of safety of his State daring the Revolutionary War, and plunged into military problems with all his energy. In 1776 he was made a member of the assembly of Pennsylvania, the earliest under the reorgan ized Revolutionary movement, and was active in the creation of the new constitution, the first for the State of Pennsylvania. In 1777 and for 12 successive years he was elected State treasurer. He was also trustee of the Loan Office.
He determined the boundaries of Pennsyl vania and the line between New York and Massachusetts. From 1779 to 1782 he was pro fessor of astronomy in the University of Penn sylvania and trustee and vice-provost. In 1792 he was made director of the United States mint by President Washington. After three years he resigned and returned to scien tific work. He succeeded Franklin as president of the American Philosophical Society in 1790.
His publications (about 20) appeared in the Transactions of the Ameiican Philosophical Society. The most popular was an 'Oration on Astronomy.> An interesting was delivered after his death by Dr. Benjamin Rush. His life was written by his nephew, William Barton, in 1813, and by James Renwick in Sparks' American Biography.) An account of him, by S. W. Pennypacker, was issued in 1882.