THE EARTH A MAGNET. 39 



gradual shifting of the magnetic equator from east to 

 west along the true equator. This motion .has been 

 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 farther from Paris now that the needle is 

 inclined more than 23 from the vertical, than in 16Y1, 

 when the inclination was only 15 ? It appears obvi- 

 ous 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 " equator of least intensity," 

 but not exactly. As \ve approach the magnetic poles 



