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384
MAGNETISM, TERRESTRIAL


Those of a very rapid oscillatory character were especially numerous in the morning between 4 an 9 a.m. In the late afternoon and evening disturbances of a more regular type became prominent, especially in the winter months. In particular there were numerous occurrences of a remarkably regular éype of distulgnance, halfrrtge total number of cases ta ing pace etween 7 an 9 .m. is “ special type of disturbance ” was divisible into two phases, each lasting on the average about 20 minutes. During the first phase all the elements diminished in value, duringéthe second phase they increased. In the case of D and H the rise an fall were about equa but the rise in V was about 3% times the preceding fall. The dis: turbmg force-on the north pl0le-t0 whgch thtel gret phlpsle might be attributed was inclined ont eaveragea out5 5 e owt e orizon, the horizontal projection of its line of action being inclined about 4I°é to the north of east. The amplitude and duration of the disturbances of the “ special type ” yaried a gotéd deal; in Reveral cases the disturbing force consider ab y exceede 2007. somewhat similar type of disturbance was observed by Kr. Birkeland 9° at Arctic stations also in I9§)2-1903, and was called by him the “ polar elementary ” storm. B1rkeland's record of disturbances extends onl from October 1 O2 to March 1 0, so it is uncertain whether Y 9 9 3

“ polar elementary ” storms occur during the Arctic summer. Their usual time of occurrence seems to be the evening. During their occurrence Birkeland found that there was often a great difference in amplitude and character between the disturbances observed at place; so compeeatiyeéyhnear together ale Iceland, Nivatlembla and pitz ergen. is e im to assign the cause to e ec ric currents in the Arctic at heights not exceeding a few hundred kilometres, and he inferred from the way in which the phenomena developed that the seat of the disturbances often Eioved westward, es if regateld in some way to the sun's position. ontemporaneousy wit t e “elementary polar ” storms in the Arctic Birkeland found smaller but distinct movements at stations all over Europe; these could generally be traced as far as gombay agd Batavia, land slemetimejs as far as Christchurch New ' ealand. hree, °2 on the ot er han working up the 1902-1904 Antarctic records, discovered that during the Largerlfiisturbances of the “ sp§ {:ialtt;ép1e ”t clerreempolp/Idingtbut muc sma er movements were visi e a rxs c urc, auri ius Kolaba, and even at Kew. He also found that in the great majority of case? § he< Antgrcticlcurves werelspeeuilly disglilirbiedt diérmg the timeso ir e an 's' e ementary po ar s orms e is ur ancesm the Arctic and Antarctic being of the same drder of magnitude, though apparently of considerably digeiient tyége. Examining the more prominent o the su en commencements of magnetic disturbances in 1902-1903 visible simultaneously in the curves from Kew, Kolaba, Mauritius and Christchurch, Chree found that these were all represented in the Antarctic curves by movemefits of a ebonsielerablylgagger sge fend ofi an oeeillatoiy character. nanum ero cases ir can 0 serve sma simu aneous

movements in the curves of his co-operating stations, which appeared to be at least sometimes decidedly larger (in the)equat0r1al than the northern temperate stations. These he escri ed as equatorial perturbations, ascribing them to electric currents in or near the plane of the earth's magnetic equator, at heights of the order of the earth's radius. It was found, however, by Chree that 1n many, if not all, of these cases there were synchronous movements in the Antarctic, similar in type to those which occurred simultlaneoltllsly Avvith the sudden commencements of magnetic storms, and t at t ese ntarctic movements were considerably larger than those described by Birkeland at the equatorial stations. This result tends of course to suggest a somewhat different explanation from B1rkeland's: But until our knowledge of facts has received considerable additions all explanations must be of a somewhat hypothetical character.

In 1831 Sir James Ross” observed a dip of 89° 59' at 7O'i 5' N., 96° 46' W., land th1e1has been accepted ashpracticallyrelhe position 0; t e nort magnetic po e at the time. e position 0 lPZ~'>';'°“° the south magnetic pole in 1840 as deduced from the e ° Antarctic observations made by the Erebus and “ Terror " expedition is shown in Sabine's chart as about'73° 30' S3 147° 30' E. In the more recent chart in ]. C. Adamss Collecte Pa crs, vol. 2, the position is shown as about 73° 40' S., 147° 7' E. P

Of late years positions have bpen obtained for the soutlalsiagnegc pole by the “ Southern Cross ' expedition of 1898-1900, by t e “ 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., 1563251 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 “ Disc0very'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 euqface cart; pirobagly claim tolpega, rréagnetic pole in the sexgse ptlppar y ascri e to e term. e iurna motion were a so u e y 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'Observotoire Physique Central), the French (Annales du Bureau Central Météorologique dc France), and those of Kew, Greenwich, Falmouth, Stonyhurst, Potsdam, Wilhelmshaven, de Bilt, Uccle, O'Gyalla, Prague, Pola, Coimbra, San Fernando, Capo di Monte, Tiliis, 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 ]. Hann and G. Hellman; P.R S. =Proceedings of the Royal Society of London; P T.=Philosophical T transactions; R. =Repertorium fur Meteorolagie, St Petersburg; T.M. = Terrestrial Magnetism, edited by L. A. Bauer; R.A.S. N0tices=Monthly Notices of the Royal Astronomical Society. Treatises are referred to by the numbers attached to them; e.g. (I) p. 100 means p. 100 of Walker's Terrestrial Magnetism.

1 E. Walker, Terrestrial and Cosmical Magnetism (Cambridge and London, 1866). 12 H. Lloyd, A Treatise on Magnetism General and Terrestrial (London, 1874). 2 E. Mascart, Traité de magnétisme terrcstre (Paris, 1900). 3 L. A. Bauer, United States Magnetic Declination T ablcs and Isogonic Charts, and Principal Facts relating to the Earth's Magnetism (Washington, 1902). 4 Balfour Stewart, “ Terrestrial Magnetism ” (under “ Meteorology ”), Ency. brit. 9th ed. BC. Chree, “ Magnetism, Terrestrial, ” Ency. brit. 10th ed. 2 M.Z. 1905, 23, 145. 7(3) p. 62. SK. Akad. van Wetenschappen (Amsterdam, 1895; Batavia, 1899, &c.). 9 Atlas des Erdmagnetismus (Riga, 1903). 1° (1) p. 16, &c. 11 Kolaba (Colaba) Itlagnetical and Meteorological Observations, 1896, Appendix Table II. 12(1) p. 21. 13 Report for 1906, App. 4, seealso (3) p. 102'. 14(1) p. 166. 15 Ergebnisse der mag. Beobachtungen in Potsdam, 1901, p. xxxvi. 1° U.S. Coast and Geodetic Survey Report for 1895, App. I, &c. 17 T.M. 1, pp. 62, 89, and 2, p. 68. 12 (3) p. 45. 1° Die Elemente des Erdmagnetismus, pp. 104-108. 2° Zur tdglichen Variation der mag. Deklination (aus Hefl II. des Archivs des Erdmagnetismus) (Potsdam, 1906). 21M.Z. 1888, 5, p. 225. 22M.Z. 1904, 21, p. 129. 22 P.T. 202 A, p. 335. 22" Comb. Phil. Soc. Trans. 20, p. 165. 24 P.T. 208 A, p. 205. 25 P.T. 203 A, p. 151 2° P.T. 171. p. 541; P.R.S. 63, p. 64. 27R.A.S. Notices 60, p. 142. 2° Rendiconti del R. 1st. Lomb. 1902, Series II. vol. 35. 29 R. 1889, vol. 12, no. 8. 3° B.A. Report, 1898, p. 80. 21 P.R.S. (A) 79, F. 151. 12 P.T. 204 A, p. 373. 33 Ann. du Bureau Central Météoroogique, année 1897, 1 Mem. p. B65. 24 P.T. 161, p. 307. 35 M.Z. 1895, 12, p. 321. 25° P.T. 1851, p. 123; and 1852, p. 103, see also (4) § 38. 3° P.T. 159, p. 363. 37 (1) p. 92. “R.A.S. Notices 65, p. 666. 3° R.A.S. Notices, 65, pp. 2 and 538. 4° K. Akad. van Wetcnschappen (Amsterdam, 1906) p. 266. 41 R.A.S. Notices 65, p. 520. 42B.A. Reports, 1880, p. 201 and 1881, p. 463. 42 Anhang Ergebnisse der mag. Beob. in Potsdam, 1896. 44 M.Z. 1899, 16, p. 385. 45 P.T. 166, p. 387. 4° Trans. Can. Inst. 1898-1899, p. 345, and Proc. Roy. Ast. Soc. of Canada, 1902-1903, p. 74, 1904, p. xiv., &c. 47 R.A.S. Notices 65, p. 186. 42 T.M. 10, p. 1. '° Expéditian norvégienne de 1899-1000 (Christiania, 1901). 5° Theses présentées d la Faculté des Sciences (Paris, 1903). 51 Nat. T ijdschrift voor Nederlandsch-Indié, 1902, p. 71. 22 Wied. Ann. 1882, .p. 3 6. 53 Sitz. der k. preuss. Akad. der Wiss., 24th June 1897, gcc. 54 T.M. I2, p. I. 55 P.T. 143, p. 549; St Helena Observations, vol. ii., p. cxlvi., &c., (1) § 62. “Trans R.S.E. 24, 669. "P.T. 178 A, p. 1. 5° Batavia, vol. 16, &c.' 59 Batavia, Igppendix to vol. 26. 6° R. vol. 17, no. 1. 62 T.M. 3, p. 13, &c. °2P.T. 181 A, p. 53 and 188 A. 63 Ann. du Bureau Central Mét. vol. i. for years 1884 and 1887 to 1895. 64 Ann. dell' Uf. Centrale Met. e Geod. vol. 14, pt. i. p. 57. °5 A Magnetic Survey of the Netherlands for the Epoch 1st Jan. 1891 (Rotterdam, 1895). 6° Kg. Svenska' Vet. Akad. Handlingar, 1895, vol. 27, no. 7. 67 Denkschriften der math. naturwiss. Classe der k. Akad. des Wiss. (Wien), vols. 62 and 67. “B Journal of the College of Science, T okyo, 1904, vol. 14. 2° Ann. de Vobservatoire de Toulouse, 1907, vol. 7. 7° Ann. du Bureau Central Mét. 1897v I. p. B36. 71 T.M. 7, p. 74. "2Bull. Imp. Univ. Odessa 85, p. 1, and T.M. 7, p. 67. 73 P.T. 187 A, p. 345. 74 P.R.S. 76 A, p. 181. 75 Bull. Soc. Imp. des Naturalistcs de Moskau, 1893, no. 4, p. 381, and T. M . 1, p. 50. 1° Forsch. zur deut. Landes- u. Volkskundc, 1898, Bd. xi, 1, and T.M. 3, p. 77. 77 P.R.S. 76 A, p. 507. 7° Adams, Scientijic Papers, II. p. 446. 7° B.A. Report for 1898 p. 1 8°Abhand. der bayer. Akad. der Wiss., 1895, vol. 19. 21 Sitz. k. Aogad. der Wiss. (Berlin), 1897, no. xviii., also T.M. 3, p. 191. 22 T.M. 2, p. I 1. 23 Die Elemente des Erdmagnetismus (St Petersburg.