POWERHOUSE COLLECTION

Thacher cylindrical slide rule

Object No. B1133

This is a very accurate desk-top slide rule of a type used to perform calculations between 1881 and the 1960s, when electronic calculators became available. Slide rules are analog devices that the user manipulates to add and subtract the logarithms of the numbers involved in a calculation. The first cylindrical slide rule, with extra long logarithmic scales to provide greater accuracy, was introduced by Irishman George Fuller in 1879. Edwin Thacher's 1881 design set new standards in accuracy by pushing computations to four digits. This feat was accomplished by dividing up a very long linear rule into equal lengths and arranging the pieces around a cylinder with a barrel slide. Sometimes referred to as a 'squirrel cage' slide rule, its use of both rotary and longitudinal movement gave the rule an effective length nearly 40 times greater than that of an ordinary slide rule. By 1897 the New York company of Keuffel & Esser had taken over production of Thacher's slide rules and, in a curious footnote to history, misspelled his name 'Thatcher' for the entire life of their production. Geoff Barker, March 2007 References Baxandall, D., 'Calculators Machines and Instruments, Science Museum, 1975 Wynter, H., and Turner, A., 'Scientific Instruments', Studio Vista,1975 Kidwell, P., and Ceruzzi, P., 'Landmarks in Digital Computing; a Simthsonian Pictorial History', Smithsonian Institution Press, 1994 Williams, M., 'A History of Computing Technology', Whitehall Books, Wellington, New Zealand, 1985 http://www.americanartifacts.com/smma/advert/az461.htm