Edward J. Johnson and the early History of Ship Magnetism

Abstract

During the months of October and November 1835 a series of magnetic observations was made, under orders of the Lords Commissioners of the Admiralty, on board the iron steamship Garryowen by Commander Edward J. Johnson R.N. The results of Johnson's observations paved the way to Airy's solution to the crucial problem of compass management on board an iron ship.Johnson related in a paper in which he described his experiments, that he proceeded to Ireland taking with him the necessary instruments for ascertaining the deviation of the magnetic needle produced by the local attraction of an iron steam-vessel, together with instruments for measuring dip and magnetic intensity. Every facility was afforded him by the owners of the Garryowen, the City of Dublin Steam Packet Company, and by the builders of the vessel, Messrs. Laird of Liverpool.The Garryowen, built in 1833, was a paddle steamer of length 130 ft, breadth 21 ft 6 in and depth 11 ft. She was equipped with two engines each rated at 85 h.p. and her tonnage was 281 tons burden. She was fitted with four water-tight transverse bulkheads of wrought-iron ¼ in thick. Her hull and boilers were of malleable iron and the total weight of iron in her structure amounted to 180 tons.