2'32 Proceedings of Philosophical Societies. [Maiich, 



from other circumstances, that what we call the variation of the 

 needle, is, in fact, no variation at all, so that the north-pole of 

 the earth may not, in reality, possess any magnetic attraction. 

 The situation of the pole discovered by Capt. Parry, by a rough 

 computation from the amount of the dip at various spots in its vici- 

 nity, as given by him, is at the intersection of 73° north latitude 

 and 101° west longitude. Mr. M. has ascertained, that the 

 oscillations of the needle are isochronous; and also, that when 

 the north pole of a magnet is presented to the south pole of the 

 needle, the oscillations describe segments continually decreasing, 

 but are still performed in equal times : now if the north pole of 

 the earth have any attraction, the oscillations of the needle, when 

 upon the line of no variation in the neighbourhood of the north- 

 west pole, which was crossed by Capt. Parry, ought to be accele- 

 rated on approaching it ; and by this means the fact may be 

 ascertained. 



Mr. Macdonald supposes that the north-west magnetic pole 

 has a rotatory motion, producing the two lines of no variation in 

 the northern hemisphere, and that during the 159 years, from 

 1657 to 1816, in which the needle was advancing to the west, it 

 described one-fourth of its orbit. This theory of the motion of 

 the pole, he remarked, required one objection to be obviated, — 

 the supposed solidity of the earth : but of this opinion, he 

 stated, there was no more physical proof than of the contrary 

 one ; the subject was one of the hidden secrets of God never to 

 be discovered. The Mosaic records indicate the earth to be full 

 of water, contained as in a shell ; and many passages of Scrip- 

 ture might be adduced to confirm this indication; the mode in 

 which the earth must have acquired its figure, and several astro- 

 nomical facts, likewise tend to show that it does not consist of 

 solid matter increasing in density to the centre. 



Mr. M. supposes that there is also a south-east magnetic pole, 

 by the rotation of which the two lines of no variation in the south- 

 ern hemisphere are produced ; Capt. Cook came to a spot where 

 the dip amounted to rather more than 70° ; and this pole may 

 be discovered or approximated to by sailing in the line of no 

 variation at New Holland, as far as the ice will permit. The 

 circumstance that the aurora borealis is never seen to rise, in 

 Greenland, either in the north or north-west, but in the south- 

 east or east, was cited from Crantz's History, in confirmation of 

 this idea of a south-east magnetic pole. 



In his former papers on magnetism, inserted in the Philoso- 

 phical Transactions for 1796 and for 1797, the author had 

 adopted Dr. Halley's theory of four magnetic poles ; but two of 

 these, it had since been found, did not exist where they were 

 stated to be. In those papers, likewise, he had ascribed certain 

 effects to the action of the sun's rays upon the earth, which, in 

 consequence of Sir H. Davy's electro-magnetical discoveries, he 

 was now disposed to attribute to galvanic agency ; the diurnal 



