THE SCIENTIFIC METHOD 123 



tain forms of the energy of bodies which we name 

 heat, light, etc., are observed to appear in other bodies 

 although the space between them is devoid of matter. 

 We suspect that the amount of this energy disappear- 

 ing in the emitting bodies is equal to the amount ap- 

 pearing in the receiving bodies and that time elapses 

 between the emission and the reception of the energy. 

 On these ideas we have built the theory that energy 

 travels through immaterial space and in its transit we 

 call it radiant energy. The conception of radiant 

 energy in a vacuum is a useful one if we limit it to a 

 mere quantitative idea. For this purpose it suffices to 

 state the facts in a mathematical formula which ex- 

 presses a continuous passage of a quantity of energy 

 through space equal to the amount lost by the emitting 

 body. We thereby generalize the laws of continuity 

 and conservation and of cause and effect. This is not 

 the custom ; it is usual to try to explain the nature and 

 mechanism of radiant energy. This requires either 

 that space be filled with an ether to serve as the vehicle 

 of energy or that energy be regarded as itself an 

 entity. 



It has been the persistent attempt of physicists for 

 centuries to explain this radiant energy by mechanical 

 models. And this effort has fastened on the science 

 an interminable series of impossible fictitious ethers 

 and mechanical atoms. The most indefatigable labors 

 of the greatest minds have been spent to construct an 



