David**, an eminent American astronomer, was born near Germantown in Pennsylvania in 1732, and was early put to work on his father's farm. His youth was characterised by signs of uncommon talent. Every spare moment was employed in gratifying his taste for the exact sciences. When he stopped his team on the field, he covered the plough-tails with mathematical figures. As he sauntered about in the evening after his day's labour, he pried his knife in making wooden clocks. A present of watchmaking tools, which he received at the age of eighteen, was the means of still further developing his genius. Taking up the more congenial trade of a watchmaker, he enjoyed greater opportunities for prosecuting his favourite studies. The utmost use was made of the two or three mathematical books which he had. Ere he was twenty he had begun to read the *Principia*. It is even said that he had found out the method of fluxions before he was aware of the discoveries of Newton and Leibnitz on the same subject. The attainments of Rittenhouse soon came to be generally acknowledged, and a series of honours and appointments followed. In 1769 he was named one of the committee to observe the transit of Venus over the sun's disk. In 1779 he was employed to determine the boundary line between Pennsylvania and Virginia. The Academy of Arts and Sciences at Boston elected him a member in 1782. The American Philosophical Society made him their president, in the room of Franklin, in 1791. The Royal Society of London also elected him a fellow in 1795. He was director of the mint of the United States when he was seized with his last attack of debility in 1795; and he died in June 1796. His published works consist of a number of papers, chiefly on astronomical subjects, in the *Transactions of the American Philosophical Society*.