Isaac Dalby, an English mathematician, born in Gloucestershire in 1744, died at Farn-ham, Surrey, Oct. 14, 1824. He was intended by his friends for a cloth worker, but, having fitted himself by the aid of a few mathematical books to be an usher, was employed in that capacity. Going to London in 1772, and being appointed to teach arithmetic in Archbishop Tenison's grammar school, he became known to many men of science, and was employed in making astronomical observations in a building erected for philosophical purposes by Top-ham Beauclerk. When this establishment was broken up, after being employed in several similar institutions, he became mathematical master of the naval school at Chelsea. In 1787 he assisted Gen. Roy in taking the trigonometric observations for connecting the meridians of Greenwich and Paris, and for two years was occupied in extending the triangula-tions through Kent and Sussex to the coast. Gen. Roy died in 1790, and the next year Dalby was engaged together with Col. "Williams and Capt. Mudge to continue the survey of England. They began by remeasuring the original base lino on Hounslow heath, and under their care the triangulation was extended to Land's End. On the formation of the military college at High Wycombe in 1799, Dalby was appointed professor of mathematics in the senior department, and held that office till 1820. He was the author of mathematical papers and reports, and of a "Course of Mathematics" in 2 vols.