THE EARTH A MAGNET. 31 



found to be really taking place. It is supposed that 

 the movement is accompanied by a change of form ; 

 but more observations are necessary to establish this 

 interesting point. 



Can it be doubted that while these changes are 

 taking place, the magnetic poles also are slowly shifting 

 round the true pole ? Must not the northern pole, for 

 instance, be further from Paris now that the needle is 

 inclined more than 23 from the vertical, than in 1671, 

 when the inclination was only 15. It appears obvious 

 that this must be so, and we deduce the interesting 

 conclusion that each of the magnetic poles is rotating 

 around the earth's axis. 



But there is another peculiarity of the needle which 

 is as noteworthy as any of those we have spoken 

 about. We refer to the intensity of the magnetic 

 action the energy with which the needle seeks 

 its position of rest. This is not only variable from 

 place to place, but from time to time, and is further 

 subject to sudden changes of a very singular character. 



It might be expected that where the dip is greater, 

 the directive energy of the magnet would be propor- 

 tionately great. And this is found to be approximately 

 the case. Accordingly, the magnetic equator is very 

 nearly coincident with the e equator of least intensity,' 

 but not exactly. As we approach the magnetic poles 

 we find a more considerable divergence, so that instead 

 of there being a northern pole of greatest intensity 

 nearly coincident with the northern magnetic pole, 

 which we have seen lies to the north of the American 



