Dialling (mathematics)

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In somewhat archaic applied mathematics, dialling is the mathematics required to create a sundial face to determine solar time based on the position of the sun. Those skilled in the art were referred to as dialists or gnomonists, the latter derived from the word gnomon, which was a device that used a shadow as an indicator.

The mathematician William Oughtred published a book, Easy Method of Mathematical Dialling, around 1600.[http://www.answers.com/topic/william-oughtred?cat=technology Answers article about William Oughtred] Samuel Walker (1716–1782) was a Yorkshire mathematician and diallist.Index of British Mathematicians Part III 1701–1800 by Ruth V & Peter J Wallis (published by University of Newcastle upon Tyne?) In his later years, Thomas Jefferson was known to practice dialling as a mental exercise.{{Cite web |url=http://www.math.virginia.edu/Jefferson/jeff_r(3).htm |title=a letter from Mr. Jefferson to Charles Clay in 1811 |access-date=15 July 2007 |archive-url=https://web.archive.org/web/20070712102800/http://www.math.virginia.edu/Jefferson/jeff_r(3).htm |archive-date=12 July 2007 |url-status=dead }} Professor of astronomy at Gresham College (London, UK), Samuel Foster (d. 1652), developed reflex dialling, which describes a device of his own invention: a sundial capable of reflecting a spot of light onto the ceiling of a room.Miscellanies: or, mathematical lucubrations by Samuel Foster, edited by John Twysden (1607–1688), published 1659 in London by R. & W. Leybourn