36 



MAGNETISM. 



3. Correction of jfipinus's Theory. 



(148.) Thus far do the facts accord with 

 the hypothesis of ^Epinus, and thus far 

 may we admit that hypothesis to be a sa- 

 tisfactory explanation of these facts. But 

 in one important application it entirely 

 fails; it does not explain the consequences 

 that are observed to follow on the division 

 of a magnet at the neutral point. Theory 

 would lead us to expect that we should, 

 in this case, obtain the different polari- 

 ties separate, one in one piece, and the 

 other in the other. The fact we know to 

 be totally different: each part becomes 

 a regular magnet with two poles, one of 

 which retains the character it had before 

 the separation. ' 



,/Epinus attempted to remove this dif- 

 ficulty by supposing that, in the act of 

 fracture, a portion of the fluid actu- 

 ally escaped from the overcharged pole, 

 while another portion entered into that 

 which was undercharged, effects which 

 he conceived might result from the 

 sudden change in the balance of mag- 

 netic forces consequent upon the frac- 

 ture. But this explanation, as Professor 

 Robison remarks, is far from satisfac- 

 tory. 



(149.) The only rational mode of re- 

 conciling this fact with the system of 

 yEpinus, is to consider a magnet as an 

 aggregate of small particles of iron, each 

 of which individually has the properties 

 of a separate magnet ; that is, has two 

 poles of its own: the arrangement of 

 these particles being such that all the 

 poles are disposed in a regular order of 

 alternation ; so that in every part of the 

 mass of iron, each pole of one particle is 

 in contact with the contrary pole of the 

 next in the series. These adjacent poles 

 of course neutralize one another, with 

 regard to their magnetic action, and it 

 is only those which are situated at the 

 extremity of the line, and which are not 

 associated with any other, that consti- 

 tute the active poles of the entire mag- 

 net. Hence it is at the surface, and 

 more particularly at the extremities, 

 that polarity is manifested; and hence 

 when a magnet is broken across, the 

 fractured ends at once exhibit the oppo- 

 site polarities they had before possessed, 

 but which had been masked by their 

 cohesion. 



(150.) A practical illustration of this 

 view of the subject may be afforded by 

 placing a number of small magnets of 

 equal strength in a line, with their oppo- 

 site poles in contact, as exhibited in fig. 



41. It will be found that almost the 

 only polarity that^is sensible, appears 



Fig. 41. 



Stl, _ t ^^_ 



at the two extremities N and S ; the 

 intermediate portions formed by the 

 junction of the opposite poles n and s 

 being, to all appearance, neutral. If the 

 series be broken at any one point as at 

 F, the two portions G and H will imme- 

 diately present the properties of separate 

 magnets, and the new poles N 1 and S 1 

 being now separated, exhibit their na- 

 tural activity. 



(151.) According to this view of the 

 subject, the induction of magnetism will 

 consist, not in the actual transference of 

 the magnetic fluid from one extremity 

 to the other of the iron bar which has 

 been rendered magnetic ; but in a 

 change of this nature taking place in 

 every particle individually, and by which 

 each particle is converted into a separate 

 magnet. 



4. Theory of two Magnetic Fluids. 



(152.) The theory with respect to 

 magnetism which has of late more gene- 

 rally prevailed, is founded on the sup- 

 position, that its phenomena are occa- 

 sioned by the agency of two magnetic 

 fluids, residing in the particles of iron, 

 and incapable of quitting them ; one of 

 which fluids imparts the northern and 

 the other the southern polarity. They 

 have been denominated respectively 

 the Austral and Boreal fluids. The 

 particles of each of these two kinds of 

 fluids attract those of the other, but 

 repel those of the same kind. When in 

 combination with each other, these 

 fluids are neutral and inert; each be- 

 coming active only when separate. The 

 decomposition of the united fluids is 

 effected by the inductive influence of 

 either the one or the other when acting 

 independently. It is obvious that, as 

 far as regards the distribution and ac- 

 tion of the two magnetic fluids in each 

 individual particle, "this theory is pre- 

 cisely similar to that of the two electric 

 fluids, of which an account has been 

 already given in our Treatise on Elec- 

 tricity ; it is therefore unnecessary to 

 pursue its development in those particu- 

 lars, for the reader need only refer to 



