On /he Magfietic Power of the Poles of the Earth. 253 



to an inconceivable extent ; we have a right to infer that the 

 earth itself is magnetized by the very same means as the needle 

 in the above experiment. The road to this inference is so 

 direct, that to convince, it seems only necessary to point it out. 



It seems self-evident that the magnetic power cannot reside 

 in water either in a fluid or solid state; and it is probable 

 that it cannot be transmitted through the waters of the ocean, 

 and therefore will reside where the land predominates within 

 the arctic circle; and also for this further reason, that it is 

 there the ice naturally assumes those forms best adapted for 

 decomposing the sun's rays : hence, where this power of de- 

 composing the light is chiefly concentrated, the magnetic pole 

 will probably be found. The prevalence of land at the north 

 over that of the south pole is evidently, for these reasons, at once 

 the general cause of the positive magnetism of the former, and 

 the frequency and splendour of the aurora proceeding from it, 

 in comparison of the faint exhibition of the aurora austrahs. 



Although the magnetic pole is to be looked for where the 

 land abounds within the arctic circle ; yet its situation is most 

 probably determined by local circumstances seemingly con- 

 trary; such as the abounding of water within land, on the shores 

 of which the most powerful apparatus for decomposing light 

 will be formed. Its situation will also be affected by changes 

 incident to all climates : hence its place may change, though 

 not according to any known law. Tlie magnetic influence no 

 doubt extends over a considerable space, but the point of 

 greatest intensity will be the magnetic pole for the time. All 

 these considerations evidently point to the very spot of the 

 globe where the magnetic pole is known to be situated ; yet 

 the northern boundaries of the eastern world may possibly be 

 so much magnetized, as to attract the needle in such parts of 

 the world as are more within its sphei'e than that of the north- 

 west pole. 



There is nothing hypothetical in these theories of the atirora 

 borealis and the earth's magnetism : what constitutes a hyjio- 

 thesis is its resting on supposed facts ; or, what is worse, ascrib- 

 ing effects to causes they are not known, or known not, to pro- 

 duce. The above explanation admits of the same proof as tlie 

 <loctrine of universal gravitation both in kind and degree. Its 

 celebrated discoverer justly inferred that the planetary bodies 

 must exert a similar power on one another, to that he found 

 the earth exert on smaller bodies near its surface, because the 

 same law evidently governs both. It is with equal justice in- 

 ferred, that if one of the components of light, separated by a 

 small glass prism, has tlie power to magnetize a steel needle, 

 the same rays pi'odiiccd lo a certain extent will magnetize the 



earth 



