TERRESTRIAL MAGNETISM. 181 



observations near to the focus iu question, but on the behavior of the 

 magnet at points far distant from it in Europe and Asia. The westerly 

 march of tlie decIina;tion needle, which lasted in England up to 1818, 

 and the easterly movement which has since replaced it, are connected 

 with a supposed easterly motion of the Siberian focus, which, it is 

 added, "there is some reason to believe - - - has recently been 

 reversed." In opposition, therefore, to the idea of the rotation of a 

 magnetic focus round the geographical poles which the earlier magne- 

 ticians adopted, Stewart seems to have regarded the motion of the 

 Siberian focus as oscillatory. 



A very different aspect is put upon the matter by a comparison of 

 the magnetic maps of the world prepared by Sabine and Creak for the 

 epochs 1840 and 1880, resi)ectively. Captain Creak, having undertaken 

 to report on the magnetic observations made during the voyage of the 

 Challenger, supplemented them with the unrivaled wealth of recorded 

 facts at the disposal of the hydrographic department of the Admiralty. 

 He was thus able, by a comparison with Sabine's map, to trace the gen- 

 eral course of the secular changes all over the world for forty years. 

 The negative results may be shortly stated. There is no evidence of 

 any motion either of magnetic pole or focus. The positive conchisions 

 are still more curious. There are certain lines on the surface of the 

 earth toward which in the interval under consideration the north pole 

 of the needle was attracted. From each side the compass veered or 

 backed toward them. Above them the north pole of dip needle moved 

 steadily down. 



There are other lines frqm which, as tested by compass and dip circle, 

 a north pole was in like manner repelled. The two principal points 

 of increasing attraction are in China and near Cape Horn; the chief 

 points of growing repulsion are in the north of Canada and the Gulf of 

 Guinea. 



I am sure that my friend Captain Creak would be the first to urge 

 that we should not generalize too hastily from this mode of present- 

 ing the facts, but there can be no doubt that they can not be explained. 

 by any simple theory of a rotating or oscillating pair of poles. Prima 

 facie they suggest that the secular change is due not so much to changes 

 at the principal magnetic points as to the waxing and waning of the 

 forces apparently exerted by secondary lines or points of attraction or 

 repulsion. 



All down the west coast of America, close, be it noted, to one of the 

 great lines of volcanic activity, north hemisphere magnetism has since 

 1840 been growing in relative imi^ortance. Near Cape Horn a weak 

 embryonic pole is developing of the same kind as the well-known i^ole 

 at the other end of the continent near Hudson Bay. Along a line which 

 joins Newfoundland to the Cape of Good Hope precisely the reverse 

 effects have been experienced; while in the Gulf of Guinea a south 

 hemisj)here pole is growing within the Tropics. Of course I do not 



