ELECTRICAL INDUCTION IN A MOVING 1JODY. 211 



from its importance. This magnetism seems to have been 

 regarded as part of the original nature of things, just like 

 gravity, or the heat of the sun, as a cause from which 

 other phenomena might result, but not as itself the result 

 of other causes. 



Yet, when we come to think of it, it has none of the 

 characteristics of a fundamental principle. It appears in- 

 timately connected with other things ; and when two sets 

 of phenomena have a relation to each other, there is good 

 reason for believing them to be connected, either as parent 

 and child or else as brother and sister — the one to be 

 derived from the other, or else both of them to spring 

 from the same cause. 



Now the direction of the earth's magnetism bears a 

 marked relation to the earth's figure ; and yet it can have 

 had no hand in giving the earth its shape, which is fully 

 explained as the result of other causes ; therefore we must 

 assume that the figure of the earth has something to do 

 with its magnetism, or, what is more likely, that the ro- 

 tation which causes the earth to keep its shape, also causes 

 it to be magnetic. 



If this is the case, then there must be some influence 

 at work with which we are as yet unacquainted — some 

 cause which, coupled with the rotation of the earth, results 

 in magnetism. From the influence which the sun exerts 

 on this magnetism we are at once led to associate it with 

 this cause. Yet the cause itself cannot be the result of 

 either the sun's heat, light, or attraction. What other 

 influence, then, can the sun exert on the earth ? 



The analogy between the magnetism produced in a 

 spinning top by the inductive action of a distant body 

 charged with electricity, and the magnetism in the rota- 

 ting earth, probably caused by the influence of the sun, 

 which influence is not its mass or heat, seems to me to 

 suggest what the sun's influence is. If the sun were 



