Abstract
THE author began by referring to the results established by Gauss in 1839. Gauss proved: “(1) That the knowledge of Y (the west component of the horizontal component of terrestrial magnetism, called usually X) over the whole earth, along with the knowledge of H (the north component of H) at all points on a line running from one pole to the other, is sufficient for the foundation of a complete theory of the magnetism of the earth. (2) That a finally complete theory was also deducible from the simple knowledge of Z (the component of the earth's magnetism, that is directed to the earth's centre) on the whole earth's surface.” There existed, for a large part of the earth's surface, data for large charts of the normal values of the declination of H and of Z, at the epoch 1880, from which X, Y, and Z could readily be deduced. These charts were accurate for the zone lying between 60° N. and 50° S. lat. (except for some parts of North Asia and of Central Africa); they were less accurate for 60° to 70° N. lat., and 50° to 60° S. Beyond these limits in the south, lay regions almost un-visited since Ross's Expedition in 1840–43; so that the charts were correspondingly weak in those latitudes. The charts show that the Challenger crossed the Antarctic Circle about the meridian 79° E. These and other somewhat recent observations made between 50° and 60° S. lat., show that considerable changes in the magnetic elements have occurred since Ross's time, and therefore the charts for 1880 cannot be completed, especially as our knowledge of the changes is too limited to permit of the use of Ross's observations. Further it is desirable to have actual verification of Gauss's extension by theory of the magnetic elements at places where they are known to places where they are unknown. The position of the south magnetic pole is still undetermined, and magnetic observations are wanted from 40° S. to the geographical pole. For the carrying out of these views, Melbourne Observatory, being furnished with the necessary instruments, would serve admirably as a base station, with subsidiary bases at the Cape, and at Sandy Point, Magellan Strait, for the use of portable absolute instruments. Much of the survey could be done on board ship at sea, observations having now become so trustworthy by the process of “swingingship.” Portable instruments could also be used on ice, where their readings would be specially free from sources of error. The great effect of the ship's iron in high latitudes can be got rid of by experience, as proved in the voyage of the Challenger, an important matter being a proper position on board far the instruments. This position could be chosen immediately after the selection of the ship. The error in the vertical component varies with the “heel” of the ship; the horizontal error can be eliminated by the process of “swinging.”
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Antarctic Exploration 1 . Nature 34, 634–635 (1886). https://doi.org/10.1038/034634a0
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DOI: https://doi.org/10.1038/034634a0