In 1831 Sir James Ross[94] observed a dip of 89° 59′ at 70° 5′ N., 96° 46′ W., and this has been accepted as practically the position of the north magnetic pole at the time. The position of the south magnetic pole in 1840 as deduced from the Magnetic Poles. Antarctic observations made by the “Erebus” and “Terror” expedition is shown in Sabine’s chart as about 73° 30′ S., 147° 30′ E. In the more recent chart in J. C. Adams’s Collected Papers, vol. 2, the position is shown as about 73° 40′ S., 147° 7′ E. Of late years positions have been obtained for the south magnetic pole by the “Southern Cross” expedition of 1898-1900 (A), by the “Discovery” in 1902-1904 (B), and by Sir E. Shackleton’s expedition 1908-1909 (C). These are as follow:
| (A) 72° 40′ S., 152° 30′ E. |
| (B) 72° 51′ S., 156° 25′ E. |
| (C) 72° 25′ S., 155° 16′ E. |
Unless the diurnal inequality vanishes in its neighbourhood, a somewhat improbable contingency considering the large range at the “Discovery’s” winter quarters, the position of the south magnetic pole has probably a diurnal oscillation, with an average amplitude of several miles, and there is not unlikely a larger annual oscillation. Thus even apart from secular change, no single spot of the earth’s surface can probably claim to be a magnetic pole in the sense popularly ascribed to the term. If the diurnal motion were absolutely regular, and carried the point where the needle is vertical round a closed curve, the centroid of that curve—though a spot where the needle is never absolutely vertical—would seem to have the best claim to the title. It should also be remembered that when the dip is nearly 90° there are special observational difficulties. There are thus various reasons for allowing a considerable uncertainty in positions assigned to the magnetic poles. Conclusions as to change of position of the south magnetic pole during the last ten years based on the more recent results (A), (B) and (C) would, for instance, possess a very doubtful value. The difference, however, between these recent positions and that deduced from the observations of 1840-1841 is more substantial, and there is at least a moderate probability that a considerable movement towards the north-east has taken place during the last seventy years.
See publications of individual magnetic observatories, more especially the Russian (Annales de l’Observatoire Physique Central), the French (Annales du Bureau Central Météorologique de France), and those of Kew, Greenwich, Falmouth, Stonyhurst, Potsdam, Wilhelmshaven, de Bilt, Uccle, O’Gyalla, Prague, Pola, Coimbra, San Fernando, Capo di Monte, Tiflis, Kolaba, Zi-ka-wei, Hong-Kong, Manila, Batavia, Mauritius, Agincourt (Toronto), the observatories of the U.S. Coast and Geodetic Survey, Rio de Janeiro, Melbourne.
In the references below the following abbreviations are used: B.A. = British Association Reports; Batavia = Observations made at the Royal ... Observatory at Batavia; M.Z. = Meteorologische Zeitschrift, edited by J. Hann and G. Hellman; P.R.S. = Proceedings of the Royal Society of London; P.T. = Philosophical Transactions; R. = Repertorium für Meteorologie, St Petersburg; T.M. = Terrestrial Magnetism, edited by L. A. Bauer; R.A.S. Notices = Monthly Notices of the Royal Astronomical Society. Treatises are referred to by the numbers attached to them; e.g. (1) p. 100 means p. 100 of Walker’s Terrestrial Magnetism.
[A] For explanation of these numbers, see end of article.
[1] E. Walker, Terrestrial and Cosmical Magnetism (Cambridge and London, 1856).
*1a H. Lloyd, A Treatise on Magnetism General and Terrestrial (London, 1874).
*2 E. Mascart, Traité de magnétisme terrestre (Paris, 1900).