XIII. 

 ON PARANA aNETIG AND DIAMA GNETIG FORCES. 1 



notion of an attractive force, which draws bodies 

 JL towards the centre of the earth, was entertained 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 con- 

 ception of the force^ of gravitation. Nevertheless, if we 

 look closely at the matter, it will be seen that the mag- 

 netic force possesses characters 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 differ- 

 ence of these two forces. A body may be intensely 

 acted on by a magnet, and still no motion of translation 

 will follow, if the repulsion be equal to the attraction. 

 Previous to magnetization, a dipping needle, when its 

 centre of gravity is supported, stands accurately level ; 

 but, after magnetization, one end of it, in our latitude, 



1 Abstract of a discourse delivered in the Eoyal Institution, 

 February 1, 1856. 



