THE CONSERVATION OF ENERGY 



doctrine of conservation came upon the scene had 

 grown into authoritative positions, and were battling 

 actively for the new ideas. Confirmatory evidence 

 that energy is a molecular motion and not an " impon- 

 derable" form of matter accumulated day by day. 

 The experiments of two Frenchmen, Hippolyte L. 

 Fizeau and Leon Foucault, served finally to convince 

 the last lingering sceptics that light is an undulation; 

 and by implication brought heat into the same cate- 

 gory, since James David Forbes, the Scotch physicist, 

 had shown in 1837 that radiant heat conforms to the 

 same laws of polarization and double refraction that 

 govern light. But, for that matter, the experiments 

 that had established the mechanical equivalent of heat 

 hardly left room for doubt as to the immateriality 

 of this "imponderable." Doubters had indeed, ex- 

 pressed scepticism as to the validity of Joule's experi- 

 ments, but the further researches, experimental and 

 mathematical, of such workers as Thomson (Lord Kel- 

 vin), Rankine, and Tyndall in Great Britain, of Helm- 

 h<>ltz and Clausius in Germany, and of Regnault in 

 ice, dealing with various manifestations of heat, 

 placed the evidence beyond the reach of criticism. 



Out of these studies, just at the middle of the cen- 

 tury, to which the experiments of Mayer and Joule had 

 Ljrew the new science of thermo-dynamics. Out of 

 them also grew in the mind of one of the investigators 

 a new generalization, only second in importance to the 

 rine of conservation itself. Professor William 

 nson (Lord Kelvin) in his studies in thermo- 

 iinics was early impressed with the fact that 

 : cas all the molar motion developed through labor 

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