MAGNETISM. 



consequence of its inductive influence, 

 which converts it, for the time, into a 

 second magnet, having its poles so dis- 

 posed with relation to the first magnet, 

 that the adjacent parts have always op- 

 posite polarities ; and attraction, there- 

 fore, takes place hetween them. Thus 

 the pieces A and B, jig. 5, attract each 

 other, simply hecause the induced mag- 

 netism of the end s is of the opposite 

 kind to that of the pole N. In like man- 

 ner B and C attract each other, because 

 the polarities of the adjacent poles n and 

 s' being of a dissimilar kind, their mu- 

 tual action is attraction. With respect 

 to this ultimate effect, the inductive in- 

 fluence of either pole is exactly alike, 

 and leads to the same result. 



(26.) We may now understand the 

 reason why, when a magnet is placed in 

 a heap of iron filings, and then lifted 

 up, the filings attach themselves in clus- 

 ters to the poles, arranging themselves 

 in lines, and adhering together by a force 

 of attraction which extends from each 

 individual particle to those which precede 

 and follow it. They form, indeed, by 

 their mere juxtaposition, under the in- 

 fluence of the large magnet, a series of 

 minute magnets, of which the poles are 

 similarly situated in each, and being 

 alternately north and south, the adjacent 

 ends attract one another. 



(27.) This disposition of the poles 

 may be verified by making an experi- 

 ment of the same kind on a larger scale, 

 suspending from the end of a strong 

 magnet a piece of iron, such as a key (fig. 

 7), from the lower end of which a smaller 

 key maybe made to hang 

 in consequence of its in- 

 duced magnetism. To this 

 may be appended a still 

 smaller piece of iron, such 

 as a nail; and we may 

 thus proceed, adding piece 

 after piece, till the lower 

 one will exert only suffi- 

 cient attraction to sus- 

 tain a very small weight 

 of iron, such as a small 

 needle. The polarities of 

 the lower ends of each 

 piece, if examined previ- 

 ously to each additional 

 piece being appended to 

 it, will be found to be 

 constantly of the same 

 kind as that of the lower 

 end of the magnet from 

 which the whole is sus- 

 pended. This may be 

 ascertained by its at- 



tracting or repelling the poles of a small 

 magnetic needle balanced on a point, 

 and supported on a stand, as shown at 



(28.) The knowledge of the general 

 fact, that magnetic induction always 

 tends to produce attraction between the 

 adjacent parts of the bodies which act 

 upon each other, enables us to explain 

 many phenomena, which might other- 

 wise appear to be at variance with the 

 simple laws of attraction and repulsion 

 already stated. Thus we find that the 

 dissimilar poles of two magnets attract 

 each other with a force which is greater 

 than the repulsion exerted between the 

 similar poles of the same magnets ; and 

 this happens because, in the former 

 case, the tendency of induction is to 

 strengthen the magnetic power of the 

 adjacent dissimilar poles; but, in the 

 latter case, where the poles are similar, 

 each pole tends, by its inductive influ- 

 ence, to weaken the magnetism of the 

 other. This is exemplified in a still more 

 striking manner, when a weak magnet 

 is brought near to a much more power- 

 ful one : in which case we find that, 

 although when they are at a moderate 

 distance from each other, either pole of 

 the weaker magnet is repelled by the 

 similar pole of the strong one ; yet, if it 

 be brought very near, and especially if it 

 be made to touch the latter, it is at- 

 tracted, and will even adhere with some 

 force to the strong magnet. This effect 

 evidently results from the powerful in- 

 ductive influence of the strong magnet, 

 which, for the time, destroys the feeble 

 polarity of the weak magnet at the part 

 immediately adjacent, and impresses 

 upon it a polarity of an opposite kind : 

 whence attraction follows as a neces- 

 sary consequence of contrary polarities. 



(29.) The intensity of magnetic power 

 developed by induction in an iron bar, 

 was found by Mr. W. S. Harris to be 

 inversely as the distance of the inducing 

 pole from the adjacent end of the bar on 

 which it acts. It would also appear, 

 from the experiments of the same gen- 

 tleman *, that the intensity of the mag- 

 netism induced on the remote end of the 

 bar, is, with the same inductive power 

 acting on the nearer end, inversely as 

 the length of the bar. 



Magnetic induction is not confined in 

 its operation to any particular direction ; 

 thus a bar of iron will be rendered mag- 

 netic if placed at right angles, or at any 

 other inclination to the axis of the mag- 



* Transactions of the Royal Society of Edinburgh 

 for 1829. 



