208 TRANSFORMATION AND EQUIVALENCE OF FORCES. 



through the same medium may be established the correla- 

 tion of Heat and chemical affinity — a correlation which is 

 indeed implied by the marked influence that Heat exercises 

 on chemical composition and decomposition. 



The transformations of Electricity into other modes of 

 force, are still more clearly demonstrable. Produced by the 

 motion of heterogeneous bodies in contact, Electricity, 

 through attractions and repulsions, will immediately repro- 

 duce motion in neighbouring bodies. Xow a current of 

 Electricity generates magnetism in a bar of soft iron; and 

 now the rotation of a permanent magnet generates currents 

 of Electricity. Here we have a battery in which from the 

 play of chemical affinities an electric current results; and 

 there, in the adjacent cell, we have an electric current effect- 

 ing chemical decomposition. In the conducting wire we wit- 

 ness the transformation of Electricity into heat; while in 

 electric sparks and in the voltaic arc we see light produced. 

 Atomic arrangement, too, is changed by Electricity: as in- 

 stance the transfer of matter from pole to pole of a battery ; 

 the fractures caused by the disruptive discharge ; the forma- 

 tion of crystals under the influence of electric currents. 

 And whether, conversely, Electricity be or be not directly 

 generated by re-arrangement of the atoms of matter, it is at 

 any rate indirectly so generated through the intermediation 

 of magnetism. 



How from Magnetism the other physical forces result, 

 must be next briefly noted — briefly, because in each succes- 

 sive case the illustrations become in great part the obverse 

 forms of those before given. That Magnetism produces 

 motion is the ordinary evidence we have of its existence. In 

 the magneto-electric machine we see a rotating magnet 

 evolving electricity. And the electricity so evolved may 

 immediately after exhibit itself as heat, light, or chemical 

 affinity. Faraday's discovery of the effect of Magnetism on 

 polarized light, as well as the discovery that change of mag- 

 netic state is accompanied by heat point to further like con- 



