NATURAL PHILOSOPHY. 119 







philosophy, to refer all unusual phenomena to preternatural causes, 

 and on the like disposition in later times to introduce, or at all events 

 to develope, the notion of fluids as agents .which effected the more 

 mysterious phenomena of nature, such as light, heat, electricity and 

 magnetism, Mr. Grove, continues : Air being proved analogous in 

 many of its characters to fluids as previously known, the idea of fluids, 

 or an ether was carried on to other unknown agencies appearing to 

 present effects remotely analogous to air or gases. Sound was included 

 by some in the same category with the other affections of matter, and 

 as late as the close of the last century, a paper was written by 

 Lamarck to prove that sound was propagated by the undulations of 

 an ether. Heat was at an early period so viewed. Mr. Grove, how- 

 ever, in a communication published in 1847, shewed that what had 

 hitherto been stumbling blocks in this theory of heat, viz., the phenom- 

 ena presented by what have been called latent and specific heat, 

 might be more simply explained by the dynamic theory. His object 

 at present was to extend this view to electricity and magnetism, which 

 extension was, in his opinion, supported by many analogies. The 

 ordinary attractions and repulsions of electrified bodies present no 

 more difficulties when regarded as being produced by a change in the 

 state or relations of the matter affected, than did the attraction of 

 the earth by the sun, or of a leaden ball by the earth ; the hypothesis 

 of a fluid is not considered necessary for the latter, and need not be 

 so for the former class of phenomena. 



In the cases of heating, or ignition of a conjunctive wire, or con- 

 ducting body, through which what is called electricity is transmitted, 

 we have many evidences that the matter itself is affected, in some 

 cases temporarily, in others, permanently changed ; thus if a wire of 

 lead is ignited to fusion by a voltaic battery, the fused lead being kept 

 in a channel to prevent its dispersion, it gradually shortens, and the 

 molecules seem impressed with a force, acting transversely to a line of 

 directions, of the electricity ; at length the lead gathers up in nodules 

 which press on each other, to use a familiar illustration, as do a string 

 of figs. With magnetism we have many instances of the molecular 

 change which a ferreous or magnetic substance undergoes when mag- 

 netised. If the particles are free to move as for instance iron filings, 

 they arrange themselves symmetrically. An objection may be made 

 arising from the peculiar form of the iron filings, but Mr. Grove has 

 shown, that the supernatant liquid in which magnetic oxide had been 

 formed, and which contains magnetic particles, not mechanically, but 

 chemically divided, exhibits when magnetised a change in the arrange- 

 ment of the molecules, as may be seen by its effect on transmitted 

 light ; a molecular change is also evidenced by the note or sound pro- 

 duced by magnetism, and by other effects. 



Assuming that the molecules of iron change their position inter se, 

 upon magnetisation, then by repeated magnetisation in opposite direc- 

 tions, something analogous to friction might be produced ; and just 

 as a piece of caoutchouc when elongated produces heat, so a bar of 

 soft iron when subjected to rapid changes in its magnetic state, might 

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