and on the Theory of Magnetism. 93 



or helix, and where the motive power may be considered perhaps 

 as most concentrated, is in the helix at the extremity of its axis, 

 and not any distance in from the end ; whilst in the most regular 

 magnets it is almost always situate in the axis at some distance 

 in from the end : a needle pointing perpendicularly towards the 

 end of a magnet is in a line with its axis, but perpendicularly 

 to the side it points to a spot some distance from the end, whilst 

 in the helix, or cylinder, it still points to the end. This varia- 

 tion is, probably, to be attributed to the distribution of the ex- 

 citing cause of magnetism in the magnet and helix. In the 

 latter, it is necessarily uniform every where, inasmuch as the 

 current of electricity is uniform. In the magnet it is probably 

 more active in the middle than elsewhere : for as the north pole 

 of a magnet brought near a south one increases its activity, and 

 that the more as it is nearer, it is fair to infer that the similar 

 parts which are actually united in the inner part of the bar, have 

 the same power. Thus a piece of soft iron put to one end of a 

 horse -shoe magnet, immediately moves the pole towards that 

 end ; but if it be then made to touch the other end also, the 

 pole moves in the opposite direction, and is weakened ; and it 

 moves the farther, and is made weaker as the contact is more 

 perfect. The presumption is, that if it were complete, the two 

 poles of the magnet would be diffused over the whole of its mass, 

 the instrument then exhibiting no attractive or repulsive powers. 

 Hence it is not improbable that, caused by some induction, a 

 greater accumulation of power taking place in the middle of the 

 magnet than at the end, may cause the poles to be inwards, 

 rather than at the extremities. 



A third difference is, that the similar poles of magnets, though 

 they repel at most distances, yet when brought very near to- 

 gether, attract each other. This power is not strong, but I do 

 not believe it is occasioned by the superior strength of one pole 

 over the other, since the most equal magnets exert it, and since 

 the poles as to their magnetism remain the same, and are 

 able to take up as much, if not more, iron filings when together, 

 as when separated ; whereas opposite poles, when in contact, do 



