JOSEF STEFAN AND LUDWIG BOLTZMANN 355 



These results, which are in the first place stated in the 

 form of curves - for every temperature a curve with the 

 wave-length as abscissa and the energy as ordinate - can only 

 be interpreted if we succeed in summarising these curves by 

 means of an equation in the manner of Descartes, which 

 equation would then allow us, conversely, to deduce all the 

 results of observation with the exactness of the original data. 

 The production of this equation, and its interpretation, only 

 succeeded after much trial, in spite of Boltzmann's excel- 

 lent preliminary research, for the phenomena which are 

 concerned in the radiation of a solid body are very compli- 

 cated. 



But the result was something entirely new and unexpected. 

 As a basis we have a fact given by Maxwell's theory, which 

 had already been confirmed by Hertz, and by our knowledge 

 of the structure of matter from molecules and atoms, the un- 

 ordered motion of which constitutes the heat contained in 

 the body; the fact namely, that the radiating black body is to 

 be regarded as a mass of electric oscillators or wave genera- 

 tors. These are able to respond to, and absorb, every pos- 

 sible wave-length, and are likewise able to emit all possible 

 wave-lengths, in accordance with Kirchhoff 's law; for this is 

 the significance of the 'blackness' of the body. In radiating, 

 they draw the necessary energy from the heat content of the 

 body. The question was: how in these circumstances do the 

 atoms operate as radiators, so that the actual result found by 

 observation for the distribution of energy is produced ? 



The answer towards which Boltzmann's calculations con- 

 cerning discontinuous or quantum-like energy distribution 

 had already pointed the way, was, if we now add the interpre- 

 tation derived from the most recent research, as follows. 

 Every atom radiates with the wave-length or frequency which 

 is characteristic of it, but it does not radiate quantities of 

 energy of any amount, but only multiples of definite quan- 

 tities (quanta), so that it does not radiate until it has taken up 



