XIII. 



ON PARAMAGNETIC AND D1AGMAGNETIC 

 FORCES* 



THE notion of an attractive force, which draws 

 bodies towards the centre of the earth, was en- 

 tertained by Anaxagoras and his pupils, by Democritus, 

 Pythagoras, and Epicurus; and the conjectures of these 

 ancients were renewed by Galileo, Huyghens, and 

 others, who stated that bodies attract each other as a 

 magnet attracts iron. Kepler applied the notion to 

 bodies beyond the surface of the earth, and affirmed the 

 extension of this force to the most distant stars. Thus 

 it would appear, that in the attraction of iron by a 

 magnet originated the conception of the force of gravi- 

 tation. Nevertheless, if we look closely at the matter, 

 it will be seen that the magnetic force possesses char- 

 acters strikingly distinct from those of the force which 

 holds the universe together. The theory of gravitation 

 is, that every particle of matter attracts every other 

 particle; in magnetism also we have attraction, but we 

 have always, at the same time, repulsion, the final 

 effect being due to the difference of these two forces. 

 A body may be intensely acted on by a magnet, and 

 still no motion of translation will follow, if the repul- 

 sion be equal to the attraction. Previous to magnetiza- 

 tion, a dipping needle, when its centre of gravity is 

 supported, stands accurately level; but, after magnet- 

 ization, one end of it, in our latitude, is pulled towards 



* Abstract of a discourse delivered in the Royal Institution, 

 February 1, 1856. 



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