Schiehallion (or Schiehallien or Schehallien) is an isolated conical mountain (or narrow ridge??), 3554 ft high, in Perthshire (now Perth & Kinross), about 20 km west of Pitlochry. In 1772, the astronomer Royal, Nevil Maskelyne, asked the RS for advice and they appointed a Committee of Attraction (with Maskelyne and Cavendish as leading members) to advise on how to determine G from the deflection of a plumb line (or pendulum) near a mountain. This was the mountain selected and Maskelyne carried out observations here in 1774-1776 (or Jul-Nov 1774). The calculations were carried out by Hutton (following suggestions of Cavendish) and found that the density of the Earth was about 4.48 (later revised to 4.713, still much too low) - see ["Mean density of the earth", Phil. Trans. 1778] and a similar paper of 1821. Maskelyne was awarded the Copley Medal of the RS for this work. It is claimed that one of the surveyors, named Hutton (the same one??), invented contour lines during the associated mapping. (However Halley used isogonal lines in a map of magnetic variation in 1702.) There is a plaque in the car park in the Braes of Foss. [Mackinnon; Proctor; Anon, Memoir of the late Dr. Hutton; Stewart.]
Playfair investigated the rocks of the mountain in more detail in 1811 leading to a further revision to 4.87. [Berry, pp.163-164.] Cf Edinburgh.
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The Mathematical Gazetteer of the British Isles
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