VIII 

 THE CONSERVATION OF ENERGY 



A 5 we have seen, it was in 1831 that Faraday opened 

 up the field of magneto - electricity. Reversing 

 the experiments of his predecessors, who had found 

 that electric currents may generate magnetism, he 

 showed that magnets have power under certain cir- 

 cumstances to generate electricity; he proved, indeed, 

 the interconvertibility of electricity and magnetism. 

 Then he showed that all bodies are more or less subject 

 to the influence of magnetism, and that even light 

 may be affected by magnetism as to its phenomena of 

 polarization. He satisfied himself completely of the 

 true identity of all the various forms of electricity, and 

 of the convertibility of electricity and chemical action. 

 Thus he linked together light, chemical affinity, mag- 

 netism, and electricity. And, moreover, he knew full 

 well that no one of these can be produced in indefinite 

 supply from another. "Nowhere," he says, "is there 

 a pure creation or production of power without a corre- 



ling exhaustion of something to supply it." 

 When Faraday wrote those words in 1840 he was 

 treading on the very heels of a greater generalization 

 than any which he actually formulated ; nay, he had it 

 fairly within his reach. He saw a great truth with< ait 

 fully realizing its import; it was left for others, ap- 



2 53 



