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72 that of Venus, but still of importance. Observations of it were made by Rittenhouse, Smith, Lukens, and Owen Biddle, and were published by the American Philosophical Society. The following year he calculated the elements of the motion and the orbit of a comet then visible, showing himself, by comparison with European investigators engaged in the same task, capable of performing the most difficult of computations in physical astronomy, and adding to his already extended reputation. In fact, these achievements had given him so wide a fame that his powers could no longer remain pent up in Norriton, and with the prospect of many advantages both in the way of his handiwork and of his science, he removed to Philadelphia, the American centre of learning and intelligence. He still gained his livelihood by mechanical labor, and it is curious to find him as late as 1775 assuming charge, at a small salary, of the State-house clock. About this time the almanacs of the day began to announce to their readers that, “as to the calculations, I need only inform the public they are performed by that ingenious master of mathematics, David Rittenhouse, A. M., of this city, etc.” And “our kind customers are requested to observe that the ingenious David Rittenhouse, A. M., of this city, has favored us with the astronomical calculations of our almanac for this year; therefore they may be most firmly relied on.” Soon after his removal his wife died, and in December, 1772, he married Hannah Jacobs, a member of a distinguished and influential Quaker family in Chester and Philadelphia counties. In 1771 he made some experiments on the electrical properties of the gymnotus; in 1772, after constructing the necessary instruments, he and Samuel Rhoads, for the Assembly of Pennsylvania, surveyed and ascertained the levels of the lands lying between the Susquehanna and the Delaware, with a view