George Sinclair (mathematician)

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George Sinclair (Sinclar) (d. 1696) was a Scottish mathematician, engineer and demonologist. The first Professor of Mathematics, Glasgow, he is known for Satan's Invisible Works Discovered, (c. 1685), a work on witchcraft. He wrote in all three areas of his interests, including an account of the "Glenluce Devil", a poltergeist case from c. 1654, in a 1672 book mainly on hydrostatics and dealing also with coal.


He was probably from the East Lothian area. He became a professor of the University of Glasgow, 18 April 1654, initially in a philosophy chair, then in a chair founded for mathematics. In 1655 he made descents in a diving bell off the Isle of Mull, to look at the wreck of a ship from the Spanish Armada there.[1]

He was deprived of his university post in 1666, as a Presbyterian.[2] He then worked as a mineral surveyor and engineer, and was employed in particular by Sir James Hope. He was brought in by the magistrates of Edinburgh, about 1670, to oversee piping of water from Comiston into the city.[3]

On 3 March 1691, Glasgow appointed him again to the professorship of mathematics, which had been vacant.[citation needed]

Sinclair invented an early example of a perpetual motion machine based on the principle of the siphon. He first proposed this in a Latin work on pneumatics in 1669.[4]

Glenuce Devil[edit]

In his book Satan's Invisible Works Discovered (1685), Sinclair described an alleged poltergeist incident known as the Devil of Glenluce. Sinclair described the incident as having a "usefulness for refuting atheism."[5]

The incident is described as having taken place at the house of weaver Gilbert Campbell in Glenluce during October, 1654. A beggar Alexander Agnew was refused a handout by Campbell.[6] Agnew had promised to cause the family harm and over the next two years strange phenomena was alleged to have occurred at the house. This included the mysterious cutting of warp thread, demonic voices, strange whistling noises and stones being thrown.[7] The poltergeist claims have been dismissed by researchers as a hoax. Magic historian Thomas Frost suggested that the phenomena was the result of conjuring trickery.[8] The story was given to Sinclair by Campbell's son Thomas, a philosophy student from a college in Glasgow who was living at the household. Folklorist Andrew Lang suggested that Thomas had produced the phenomena fraudulently.[9]

Historian David Damrosch has noted that Alexander Agnew commonly called the "Jock of Broad Scotland" was the first person in Scottish history to publicly deny the existence of God.[10] He was hanged at Dumfries for blasphemy on May 21, 1656.[11]


James Gregory, then a professor at the University of St Andrews, attacked Sinclair in a 1672 pamphlet The New and Great Art of Weighing Vanity, under the name of Patrick Mather or Mathers, archbeadle of the University of St Andrews. Gregory was both a Cartesian and an Episcopalian, and self-consciously invoked the Hobbes-Wallis controversy in aiming at the non-conformist Sinclair.[2] An appendix to the work, Tentamina de motu penduli et projectorum,[12] was a more important essay on dynamics, regarded by D. T. Whiteside as a probable source of Isaac Newton’s theory of resisted motion.[13] Sinclair wrote an answer to Gregory,[14] but it remained unpublished.

In 1684 he published as his own a work Truth's Victory over Error. It was in fact an English translation by Sinclair of the Latin inaugural dissertation given by David Dickson, who became Professor of Divinity, Glasgow in 1640, on the occasion in 1650 when he moved to Edinburgh. This was pointed out in short order.[15]



  1. ^  "Sinclair, George (d.1696)". Dictionary of National Biography. London: Smith, Elder & Co. 1885–1900. 
  2. ^ a b Clare Jackson, Restoration Scotland, 1660-1690: royalist politics, religion and ideas (2003), p. 187.
  3. ^
  4. ^ Povey, Thomas. (2015). Professor Povey's Perplexing Problems: Pre-University Physics and Maths. Oneworld Publications. pp. 209-210. ISBN 978-1-78074-775-0
  5. ^ Henderson, Lizanne. (2009). Fantastical Imaginations: The Supernatural in Scottish History and Culture. John Donald. p. 95
  6. ^ Lamont-Brown, Raymond. (1994). Scottish Witchcraft. Chambers. pp. 29-30
  7. ^ Seth, Ronald. (1969). In the Name of the Devil: Great Scottish Witchcraft Cases. Jarrolds. pp. 77-78
  8. ^ Frost, Thomas. (1876). The Lives of the Conjurors. London: Tinsley Brothers. pp. 108-110.
  9. ^ Lang, Andrew. (1893). Fairies and Psychical Research. In Robert Kirk. The Secret Commonwealth of Elves, Fauns and Fairies. London: David Nutt. pp. 55-56. "In this affair a boy called Thomas, a son of the unlucky householder, was clearly the agent. The phenomena were stone-throwing, beating with sticks, levitation of a plate, and a great deal of voices, probably uttered by the aforesaid Thomas."
  10. ^ Damrosch, David. (1999). The Longman Anthology of British Literature. Longman. pp. 754-755
  11. ^ Levy, Leonard Williams. (1993). Blasphemy: Verbal Offense Against the Sacred, From Moses to Salman Rushdie. University of Calinfornia Press. p. 167.
  12. ^;dir=hutto_dicti_078_en_1795;step=textonly
  13. ^
  14. ^ Cacus pulled out of his den by the heels, or the pamphlet entitled, the New and Great Art of Weighing Vanity examined, and found to be a New and Great Act of Vanity.
  15. ^  "Dickson, David (1583?-1663)". Dictionary of National Biography. London: Smith, Elder & Co. 1885–1900.