Henry Kater, an English mathematician, born in Bristol, April 16, 1777, died in London, April 26, 1835. In his youth he spent some time in a lawyer's office, but upon the death of his father in 1794 he procured a commission in a regiment stationed in India, and was for some years employed in the trigonometrical survey of that country, when he returned to England and devoted himself to scientific pursuits. He became a captain, and retired on half pay in 1814. Among his most important discoveries were the determination of the precise length of the seconds pendulum, the investigation of the diminution of terrestrial gravity from the pole to the equator, and his employment of the pendulum for the purpose of finding the minute variations of the force of gravity in different parts of a country whose substrata consist of materials having different degrees of density. In the "Philosophical Transactions" of 1825-8 appeared descriptions of his "floating collimator," an instrument of great importance to trigonometers, employed to determine the position of the line of collimation in the telescope attached to an astronomical circle. He also made some ingenious experiments on the relative merits of the Cassegrain and Gregory telescopes.

He is the author of the greater portion of the "Treatise on Mechanics " in Dr. Lardner's " Cabinet Cyclopaedia," and published "An Account of the Construction and Verification of certain Standards of Linear Measure for the Russian Government" (4to, London, 1832).