ML ISM EN T A RY MA GNKT1SM. 2 73 



cal service while we are waiting for the actual truth to 

 become known. 



The state of excitement into which iron is thrown by the 

 influence of a magnet is sometimes called " magnetization 

 by influence." More commonly, however, the magnetism is 

 said to be " induced " in the iron, and hence this mode of 

 magnetizing is called "magnetic induction." Now there 

 is nothing theoretically perfect in Nature: there is no iron 

 so soft as not to possess a certain amount of coercive force, 

 and no steel so hard as not to be capable, in some degree, 

 of magnetic induction. The quality of steel is in some 

 measure possessed by iron, and the quality of iron is shared 

 in some degree by steel. It is in virtue of this latter fact 

 that the unmagnetized darning-needle was attracted in 

 your first experiment; and from this you may at once de- 

 duce the consequence that, after the steel has been mag- 

 netized, the repulsive action of a magnet must be always 

 less than its attractive action. For the repulsion is opposed 

 by the inductive action of the magnet on the steel, while 

 the attraction is assisted by the same inductive action. 

 Make this clear to your minds, and verify it by your exper- 

 iments. In some cases you can actually make the attrac- 

 tion due to the temporary magnetism overbalance the 

 repulsion due to the permanent magnetism, and thus cause 

 two poles of the same kind apparently to attract each other. 

 When, however, good hard magnets act on each other from 

 a sufficient distance, the inductive action practically van- 

 ishes, and the repulsion of like poles is sensibly equal to 

 the attraction of unlike ones. 



I dwell thus long on elementary principles, because they 

 are of the first importance, and it is the temptation of this 

 age of unhealthy cramming to neglect them. Now follow 

 me a little farther. In examining the distribution of 

 magnetism in your strip of steel you raised the needle 

 slowly from bottom to top, and found what we called a 

 neutral point at the center. Now does the magnet really 

 exert no influence on the pole presented to its center? Let 

 us see. 



Let SN, fig. 11, be our magnet, and let n represent a 

 particle of north magnetism placed exactly opposite the 

 middle of the magnet. Of course this is an imaginary case, 



thrown into a state of temporary excitement, in virtue of which they 

 are repelled; but any attempt to explain such a repulsion by the de- 

 composition of a fluid will demonstrate its own futility. 



