MAGNETISM. 



37 



that treatise, and substituting the terms 

 austral and boreal fluids for those of vi- 

 treous and resinous electricities, will 

 find that all the- details of the electrical 

 theory will apply to that of magnetism. 

 (153.) But however the laws of the 

 theory of a double magnetic fluid may 

 be analogous or identical with those of 

 the theory of a double electrical fluid, 

 their application is somewhat different 

 in the two cases, in consequence of the 

 difference of circumstances under which 

 they act. The electrical fluids, when 

 decomposed or separated from each 

 other, are capable of being extensively 

 transferred along the particles of bodies, 

 and of being collected and accumulated 

 at the surfaces, where they have a 

 tendency to escape ; and where, if that 

 tendency exceed a certain limit, they ac- 

 tually do escape, either passing into the 

 bodies in immediate contact, or flying 

 off through the air to distant bodies. 

 In this manner each kind of fluid may 

 be separately, and in any quantity, trans- 

 ferred from one body to another. No- 

 thing of this kind takes place with 

 regard to magnetism ; the magnetic 

 fluids are never found to quit the bodies 

 to which they are attached, however small 

 those bodies, however intimate the con- 

 tact with other iron, however long the 

 contact may be continued, and however 

 powerful the forces by which the fluids 

 are impelled. The phenomena conse- 

 quent on the division or fracture of a 

 magnet lead us also to the conclusion 

 that no sensible quantity of either austral 

 or boreal fluid is ever transported from 

 one part to another of the same piece of 

 iron or steel. Hence, in order to accom- 

 modate the theory to these facts, we 

 must introduce as a new condition of 

 the hypothesis on which it is founded, 

 that within the substance of a mag- 

 netized body, the two magnetic fluids, 

 when they are decomposed by the in- 

 fluence of magnetizing forces, undergo 

 displacements to an insensible distance 

 only. 



(154.) It is not necessary to deter- 

 mine whether the extremely small 

 spaces, within which these displacements 

 and motions of the magnetic fluids are 

 restricted, be actually the same as the 

 spaces occupied by the constituent mole- 

 cules of the iron ; it is sufficient for the 

 purposes both of theory and of the cal- 

 culations founded upon that theory, that 

 they be extremely small in comparison 

 with the whole volume of the body, or 

 even with the smallest dimensions that 



ever come under the cognizance of our 

 senses. Poisson, who has given us a 

 beautiful developement of this theory*, 

 designates these very minute spaces or 

 portions of a magnetic body by the name 

 of the magnetic elements of that body. 

 There is also no necessity for making 

 any particular supposition with regard 

 to" the form or respective disposition of 

 these elements, provided we simply con- 

 sider them as insulated from each other 

 by intervals impermeable to either of 

 the magnetic fluids. 



(155.) The quantities of each kind of 

 fluid contained in every magnetic ele- 

 ment must be considered, with reference 

 to all our experiments, and to all the 

 powers we can apply, as without limit ; 

 that is to say, the forces we can com- 

 mand, in any magnetizing process, are 

 never sufficient to exhaust or separate 

 the whole of the fluids. For, when a 

 body is magnetized by the inductive in- 

 fluence of a neighbouring magnet, the 

 intensity of its magnetic state, as shown 

 by its effects, increases without limit, in 

 proportion as we employ a magnet of 

 greater force ; which, of course, implies 

 that we have not yet effected the decom- 

 position or separation of the whole quan- 

 tity of the neutral or combined fluid 

 which that body contains. In like man- 

 ner, we find it impossible to separate 

 completely the two electric fluids con- 

 tained in any particular body. 



(156.) Besides the obstacles, which 

 appear to be insuperable, to the trans- 

 mission of the magnetic fluids from 

 one magnetic element to another, there 

 must exist, in the substance of certain 

 bodies, some impediment of another 

 kind, which obstructs the motion of the 

 fluids from one part to another of the 

 same magnetic element. The effect of 

 this power, which is somewhat analogous 

 to the force of friction, is to arrest the 

 particles of both fluids in the situations 

 which they occupy; and thus to op- 

 pose, in the first place, the separa- 

 tion of these fluids, and, in the next, 

 their return to the situations from 

 which they had been displaced, and 

 where they would unite to recompose a 

 neutral, fluid. This force is termed, by 

 Poisson, the coercive force. In soft iron 

 the coercive force is either wanting, or 

 is extremely feeble ; in steel and in the 

 loadstone it is very energetic; and it 

 exists in various degrees of intensity in 



* Memoires de 1'Iustitut de France, tome v., p. 

 247. The introduction to this memoir is given in 

 the Annales de Chimie, tome xxv., p. 113. 



