60 FRAGMENTS OF SCIENCE. 



verse square of the distance between the particles, he 

 proved that the planetary motions must be what obser- 

 vation makes them to be. He showed that the moon fell 

 towards the earth, and that the planets fell towards the 

 sun, through the operation of the same force that pulls 

 an apple from its tree. This all-pervading force, which 

 forms the solder of the material universe, and the con- 

 ception of which was necessary to Newton's intellec- 

 tual peace, is called the force of gravitation. 



Gravitation is a purely attractive force, but in elec- 

 tricity and magnetism, repulsion had been always seen 

 to accompany attraction. Electricity and magnetism 

 are double or polar forces. In the case of magnetism, 

 experience soon pushed the mind beyond the bounds of 

 experience, compelling it to conclude that the polarity 

 of the magnet was resident in its molecules. I hold a 

 magnetised strip of steel by its centre, and find that 

 one half of the strip attracts, and the other half repels, 

 the north end of a magnetic needle. I break the strip 

 in the middle, find that this half, which a moment ago 

 attracted throughout its entire length the north pole 

 of a magnetic needle, is now divided into two new 

 halves, one of which wholly attracts, and the other of 

 which wholly repels, the north pole of the needle. The 

 half proves to be as perfect a magnet as the whole. 

 You may break this half and go on till further break- 

 ing becomes impossible through the very smallness of 

 the fragments; the smallest fragment is found en- 

 dowed with two poles, and is, therefore, a perfect mag- 

 net. But you cannot stop here: you imagine where 

 you cannot experiment; and reach the conclusion enter- 

 tained by all scientific men, that the magnet which you 

 see and feel is an assemblage of molecular magnets 

 which you cannot see and feel, but which, as before 

 stated, must be intellectually discerned. 



