322 FKAGMENTS OF SCIENCE. 



the north pole of the earth. The needle, however, 

 being suspended from the arm of a fine balance, its 

 weight is found unaltered by its magnetization. In 

 like manner, when the needle is permitted to float upon 

 a liquid, and thus to follow the attraction of the north 

 magnetic pole of the earth, there is no motion of the 

 mass towards that pole. The reason is known to be, 

 that although the marked end of the needle is at- 

 tracted by the north pole, the unmarked end is re- 

 pelled by an equal force, the two equal and opposite 

 forces neutralizing each other. 



When the pole of an ordinary magnet is brought 

 to act upon the swimming needle, the latter is at- 

 tracted, the reason being that the attracted end of 

 the needle being nearer to the pole of the magnet 

 than the repelled end, tha force of attraction is the 

 more powerful of the two. In the case of the earth, 

 its pole is so distant that the length of the needle is 

 practically zero. In like manner, when a piece of iron 

 is presented to a magnet, the nearer parts are attracted, 

 while the more distant parts are repelled; and because 

 the attracted portions are nearer to the magnet than 

 the repelled ones, we have a balance in favour of at- 

 traction. Here then is the special characteristic of the 

 magnetic force, which distinguishes it from that of 

 gravitation. The latter is a simple unpolar force, while 

 the former is duplex or polar. Were gravitation like 

 magnetism, a stone would no more fall to the ground 

 than a piece of iron towards the north magnetic pole: 

 and thus, however rich in consequences the supposition 

 of Kepler and others may have been, it is clear that a 

 force like that of magnetism would not be able to trans- 

 act the business of the universe. 



The object of this discourse is to enquire whether 

 the force of diamagnetism, which manifests itself as a 



