TERRESTRIAL MAGNETISM. 741 



coincide with them. Since that end of a suspended 

 magnet which points to the north is called its north 

 pole, the magnetic pole of the earth which is near the 

 terrestrial north pole is magnetically a ' south ' pole ; but 

 in practice it has been found more convenient to call the 

 magnetic pole of the earth which is near the terrestrial 

 north pole, the ' north magnetic pole ' of the earth, and 

 the opposite one, near the terrestrial south pole, the 

 ' south magnetic pole. 7 



We may conclude that the definite position which 

 a freely suspended magnet assumes, must depend 

 chiefly on the force exerted on it by that magnetic pole 

 which is nearest to it, and hence, since the various places 

 on the earth are differently situated with reference 

 to the magnetic poles, that the direction of a magnet 

 suspended in one place will differ very considerably 

 from that of a magnet at another place very distant 

 from it. If a magnetic needle is freely suspended, so 

 as to be able to set itself in its natural position, the 

 angle between the direction in which it points and the 

 direction of the geographical meridian of the place 

 where the experiment is made, is called the magnetic 

 declination of that place. In some parts of the globe 

 the north pole of a magnet declines to the east of north, 

 in others to the west of north; in the former case the 

 declination is easterly, in the latter case westerly. In 

 England the declination is westerly, and amounts in 

 London to an angle of about 20. 



The magnetic poles of the earth appear to change 

 their position on the globe in the course of time, for the 

 position of a freely suspended magnet varies from time 

 to time in the same place. 



