10 ON MAGNETISM. 



be substituted for it ; the suspension thread takes 

 exactly the same position as before. This shews that, 

 upon the whole, there is no horizontal force tending to 

 produce a motion of translation of the magnet ; and 

 therefore, if there is one force tending to draw the red 

 end towards the north, there is an equal force tending 

 to draw the blue end towards the south. 



If a small magnet, as a compass-needle, be supported 

 by two small pieces of cork and floated on water, it 

 speedily takes the north-and-south position, but it shews 

 no disposition to approach any side of the basin. 



These experiments are very important. They shew 

 either that there are different attractions from different 

 parts of the Earth upon different parts of the magnet, or 

 that attraction of the Earth on one part of the magnet 

 is accompanied with equal repulsion on another part. 

 We shall find that, without negativing the first of these 

 suppositions, other experiments shew that the second is 

 universally true : that attraction on one part of a mag- 

 net is universally accompanied with repulsion on 

 another part. And thus we arrive at the first import- 

 ant law of magnetism, the " Duality of Powers." It is 

 this duality which essentially distinguishes the force of 

 magnetism from that of gravitation : in other respects, 

 it will be seen, there is much similarity of their laws. 



10. Action of one magnet upon another. Second 

 Law of Magnetism. There is attraction between dis- 

 similar ends, repulsion between similar ends. This is 

 exhibited in various ways. Idea of poles. When one 



