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.[citation needed] 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.[citation needed]

The mathematician William Oughtred published a book, Easy Method of Mathematical Dialling, around 1600.[1] Samuel Walker (1716–1782) was a Yorkshire mathematician and diallist.[2] In his later years, Thomas Jefferson was known to practice dialling as a mental exercise.[3] 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.[4]


The word dial derives from the Latin term dialis (daily), and comes from the fact that a sundial throws a shadow related to the time of day. It was also used to describe the gear in a medieval clock which turned once per day.


  1. ^ Answers article about William Oughtred
  2. ^ Index of British Mathematicians Part III 1701–1800 by Ruth V & Peter J Wallis (published by University of Newcastle upon Tyne?)
  3. ^ a letter from Mr. Jefferson to Charles Clay in 1811
  4. ^ Miscellanies: or, mathematical lucubrations by Samuel Foster, edited by John Twysden (1607–1688), published 1659 in London by R. & W. Leybourn
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