212 ON ELECTRICAL INDUCTION IN A MOVING BODY. 



charged with negative electricity, it seems to me to follow, 

 irom what the experiments I have described establish, that 

 its inductive effect on the earth would be to render it 

 magnetic, with the poles as they actually are. 



The only other way in which the sun can act to produce 

 or influence terrestrial magnetism appears to be by its 

 own magnetism. If the sun were a magnet, it would mag- 

 netize the earth. If this is the case, the sun's poles must 

 be opposite to those of the earth. Now it follows that 

 such a condition of magnetism would, or at least might, 

 if its materials are magnetic, be caused by the rotation 

 of the sun under the inductive action of electricity in the 

 earth and planets, in exactly the same way as that caused 

 in the earth by the inductive action of the sun. As the 

 direction of rotation is the same in both bodies, and the 

 electricities of the opposite kind, the magnetism would be 

 of the opposite kind also. So that on this hypothesis it is 

 probable that the sun would act by both causes. 



When I first worked out this idea, I was not aware that 

 any thing like it had been suggested before ; but Mr. Bax- 

 endell, after having seen my experiments, noticed a review 

 of a book { On Terrestrial Magnetism/ to which he kindly 

 called my attention. The author, without making any 

 assumption with regard to the electrical condition of the 

 sun, assumes it to act on the earth's electricity precisely as 

 it would under the conditions I have described; and he 

 then proceeds to consider, not only the general features of 

 the earth's magnetism, but all its details (and this in a most 

 elaborate manner) — and to show the explanation which this 

 hypothesis offers for them, particularly for the secular varia- 

 tion of the direction of the needle. I am therefore able to 

 sneak of the hypothesis as affording an explanation of the 

 numerous variations of the earth's magnetism, as well as of 

 its general features. 



