Unpublished paper and letters, 'On the variation of the compass' by John Ross Ross describes the history of compass variation and then recounts his own experiments and observations on compass variation and terrestrial magnetism undertaken aboard HMS Isabella from May-July 1818 and aboard HMS Alexander in July 1818. Preceded by a covering letter from Ross to Sir Joseph Banks and followed by a letter providing further observations from HMS Alexander. Subject: Geodesy Communicated by the President [Sir Joseph Banks]. The Royal Society did not publish this paper as Ross planned to include it in a published narrative of his voyages. Ross' narrative was published in 1819: Ross, John. A Voyage of Discovery, made under the orders of the Admiralty, in His Majesty's Ships Isabella and Alexander, for the purpose of exploring Baffin's Bay, and inquiring into the probability of a North-west Passage. Vol. 1. London: Printed by Strahan and Spottiswoode, for Longman, Hurst, Rees, Orme, and Brown, 1819. [1818]