Edwin Thacher
Edwin Thacher is probably remembered best as the inventor of a special type of cylindrical slide rule. He patented this slide rule on the 1st November 1881 at the United States Patent Office. His patent began by saying 'Be it known that I, EDWIN THACHER of Pittsburg county of Allegheny State of Pennsylvania, have invented or discovered a new and useful Improvement in Slide-Rules'. He went on to explain why he had invented this new type of slide rule: 'The purposes of my invention are to increase the length and accuracy of scales without increasing the length of the rule and to render the use of such rule more convenient.'

Edwin Thacher was born in 1839 in a place called De Kalb, in Lawrence County, New York State, in America. His father was a doctor, but Edwin studied engineering at college. His first main job as an engineer was in 1864 as a military railway builder during the American Civil War. Later on he took up making bridges and worked for the Louis Bridge and Iron Company. A lot of his job as a bridge engineer involved doing mathematical calculations to work out how strong the steel girders and concrete beams in bridges needed to be. It was because he spent a lot of time doing calculations that he invented his cylindrical slide rule. He died in New York in 1920.