THE EARTH A MAGNET. 41 



the law discovered by Sabine ? There is one very im- 

 portant element. The position of the perihelion of the 

 earth's orbit is such that the earth is nearest to the sun 

 on about the 31st of December or the 1st of January. 

 There seems nothing rashly speculative, then, in con- 

 cluding that the sun exercises a magnetic influence on 

 the earth, varying according to the distance of the 

 earth from the sun. Nay, Sabine's results seem to 

 point very distinctly to the law of variation. For, 

 although the number of observations is not as yet very 

 great, and the extreme delicacy of the variation ren- 

 ders the determination of its amount very difficult, 

 enough has been done to show that in all probability 

 the sun's influence varies according to the same law as 

 gravity that is, inversely as the square of the dis- 

 tance. 



That the sun, the source of light and heat, and the 

 great gravitating centre of the solar system, should 

 exercise a magnetic influence upon the earth, and that 

 this influence should vary according to the same law 

 as gravity, or as the distribution of light and heat, will 

 not appear perhaps very surprising. But the discovery 

 by Sabine that the moon exercises a distinctly traceable 

 effect upon the magnetic needle seems to us a very 

 remarkable one. We receive very little light from the 

 moon, much less (in comparison with the sun's light) 

 than most persons would suppose, and we get abso- 

 lutely no perceptible heat from her. Therefore it 



