OF NATURAL PHILOSOPHY. 327 



of which, the positions of both will be disturbed, in 

 the same manner as would happen if the corre- 

 sponding parts of each repelled, and those oppositely 

 directed attracted, each other; and by properly 

 varying the experiment, it is found that they really 

 do so. If a small magnet, freely suspended, be 

 brought into the neighbourhood of a larger one, it 

 will take a position depending on the position of the 

 poles of the larger one, with respect to its point of 

 suspension. And it has been ascertained that these 

 and all other phenomena exhibited by magnets in 

 their mutual attractions and repulsions are ex- 

 plicable on the supposition of two forces or virtues 

 lodged in the particles of the magnets, the one 

 predominating at one end, the other at the other ; 

 and such that each particle shall attract those in 

 which the opposite virtue to its own prevails, and 

 repel those in which a similar one resides with a 

 force proportional to the inverse square of their 

 mutual distance. 



(366.) The direction in which a magnetic bar, or 

 needle of steel, freely suspended, places itself, has been 

 ascertained to be different at different points of the 

 earth's surface. In some places it points exactly north 

 and south, in others it deviatesfrom this direction more 

 or less, and at some actually stands at right angles 

 to it. This remarkable phenomenon, which is called 

 the variation of the needle, and which was discovered 

 by Sebastian Cabot in the year 1500, is accompanied 

 with another called the dip, noticed by Robert Nor- 

 man in 1576. It consists in a tendency of a needle, 

 nicely balanced on its centre, when unmagnetized 

 to dip or point downwards when rendered magnetic, 



