MAGNETISM. 



33 



netic attraction was ascribed by Thales 

 to the secret influence of a species of 

 mind, or soul, residing in magnets. 

 This was also the doctrine taught by 

 Anaxagoras, who extended it to many 

 other phenomena in nature. Others en- 

 deavoured to account for the attraction 

 between the loadstone and iron by the 

 vague notion of a kind of sympathy ex- 

 isting between these two bodies. In 

 later times Cornelius Gemma imagined 

 that the connexion between them" was 

 established by what he cads invisible 

 rays. Cardan asserted that the iron 

 was attracted because it was of a cold 

 nature, and Costeo de Lodi, because 

 iron was the natural food of the magnet. 



(132.) But, consigning these wild va- 

 garies to the oblivion they merit, let us 

 consider whether the phenomena of 

 magnetism are capable of being re- 

 duced to any class of physical actions 

 with which we are more "familiar. In 

 accounting for a motion which we see 

 take place, we have a natural repugnance 

 to admit of the existence of a power 

 of action at a distance ; or, in other words, 

 to conceive that a body can act where 

 itself is not: and we always incline to 

 that supposition which implies the mo- 

 tion to be the effect of impulse. We 

 naturally ask, agreeably to this prepos- 

 session, whether the movements of mag- 

 netic bodies may not be occasioned by 

 the impulse of some subtile ethereal fluid 

 impinging on their surfaces ; emanating, 

 for instance, from one end, and passing 

 into the other, or circulating in invisible 

 currents around the magnets from pole 

 to pole. This fluid might, for instance, 

 be conceived to emanate from one pole, 

 to enter at the other, and permeating 

 the substance of the magnet, again to 

 issue from its former outlet. 



Such was the train of thought that 

 obviously occurred to those who first 

 witnessed the arrangement which iron 

 filings, loosely scattered around a mag- 

 net, assume in consequence of its 

 influence. The filings have the ap- 

 pearance which would be given by a 

 stream of fluid brushing by them, 

 and turning each individual filament 

 in the direction of its course ; which 

 course might accordingly be easily 

 traced in the regular and symmetric 

 curves that are exhibited to the eye. 

 In the infancy of the science, and in the 

 absence of any other hypothesis, many 

 were the speculations advanced as to 

 the mode in which these supposed 

 streams of magnetic fluid produced the 



observed effects. Descartes was the 

 foremost among those philosophers who 

 laboured to account for all the unex- 

 plained movements in nature by the im- 

 pulsion of fluids circulating in vortices ; 

 and he naturally viewed the phenomena 

 of magnetic action as strongly corrobo- 

 rating his system. Euler also, who 

 sought to explain various natural ap- 

 pearances by the intervention of an 

 ethereal fluid, did not fail to apply his 

 favourite hypothesis to the elucidation 

 of magnetism. He even went so far as 

 to imagine the possibility of there exist- 

 ing in the substance of iron numerous 

 canals, through which the ether circu- 

 lated, furnished with valves which regu- 

 lated the direction in which it moved. 

 It was not until the phenomena had 

 been examined with greater care, and 

 were rigorously subjected to the in- 

 ductive process, that juster notions of 

 the nature of the magnetic forces came 

 to be entertained. With the knowledge 

 we now possess of the actual law of 

 magnetic attraction and repulsion, it 

 must be at once perceived that all hypo- 

 theses founded on the impulse of a fluid 

 in motion, are irreconcileable with that 

 law, and must therefore be totally dis- 

 carded. 



2. Theory of Mpinus. 



(133.) The obvious analogy which pre- 

 sents itself between the phenomena of 

 magnetism and those of electricity, na- 

 turally suggested the probability that 

 the same mode of explanation might 

 apply to both, and laid the foundation 

 of the first rational theory of magnet- 

 ism. While ^Epinus was intent upon 

 improving the beautiful electrical theory 

 of Franklin, he was struck with the re- 

 markable similarity in the attractions 

 and repulsions exhibited by the tourma- 

 line, when it is heated, to those of mag- 

 netic bodies ; and it occurred to him 

 that the phenomena of magnetism might 

 be derived from the agency of a peculiar 

 fluid, having properties very similar to 

 those of the electric fluid, but which 

 acted exclusively upon iron. The prin- 

 cipal difference between the two sets of 

 phenomena was, that, in the case 'of 

 electricity, the agent, whatever be its 

 nature, is actually transferred from one 

 body to another; but in magnetism 

 there is merely induction, but never any 

 transference. In as far, however, as 

 respects mere attraction, repulsion, and 

 induction, electricity and magnetism pre- 

 sent phenomena that are perfectly pa- 

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