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a native of Wales, and probably one of the Quaker converts who came from that country and settled a number of townships in Pennsylvania. When he was three years old, his father, Matthias, removed with his family to a farm in Norriton, now Montgomery County, and naturally enough he determined that David, the oldest son, should follow the same pursuit. As soon, therefore, as he was strong enough to be of assistance, he was put to the ordinary farm-work, and he ploughed and harrowed, sowed and reaped, like all the boys by whom he was surrounded. His tastes, however, ran in another direction, and one of those occurrences which are sometimes called accidents gave him an opportunity to gratify them. An uncle, who was a carpenter, died, leaving a chest of tools, and among them a few books containing the elements of arithmetic and geometry, and some mathematical calculations. These things, valueless to every one else, became a treasure to David, then about twelve years old, and they seem to have determined the bent of his life. The handles of his plough, and even the fences around the fields, he covered with mathematical calculations. At the age of eight he made a complete water-mill in miniature. At seventeen he made a wooden clock, and afterward one in metal. Having thus tested his ability in an art in which he had never received any instruction, he secured from his somewhat reluctant father money enough to buy in Philadelphia the necessary tools, and after building a shop by the roadside, set up in business as a clock and mathematical instrument maker. His days were given to labor at his chosen trade, and his nights to study. By too close application he injured his health, contracting an affection of the lungs, attended with great pain, that clung to him all of his life, and seriously interfered with his writing, but he solved the most abstruse