Unpublished letter, on compass variation on HMS Alexander from John Ross to Sir Jos [Joseph] Banks Ross provides further observations of compass variation on board HMS Alexander and attempts to define a rule for calculating deviation. Subject: Geodesy Written by Ross on HMS Alexander at sea. 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. 1 September 1818