3s6 GREAT MEN OF SCIENCE 



this definite amount of energy (its energy-quantum or light- 

 quantum) from its surroundings, whereupon this whole 

 amount of energy is radiated in a train of waves. The mag- 

 nitude of this energy is also proportional to the frequency of 

 the atoms; simply proportional, that is to say. This is the 

 substance of the 'quantum theory'; it was soon possible to 

 enlarge it by the hypothesis that atoms altogether only deal 

 with energy in quanta, whereby the magnitude of the quanta 

 is always proportional to a frequency (the reciprocal of a 

 characteristic time) which plays a part in the energy trans- 

 formation, the proportionality being given by a factor which 

 is always the same as that derived from the radiation of a 

 black body. 



We are here justified in speaking of a quantum theory, and 

 no longer of an hypothesis, since many processes have already 

 become capable of observation, in which this quantum-like 

 transformation of energy in the atoms occurs, and particu- 

 larly because the proportionality factor above mentioned 

 gives rise to an exactly ascertainable quantitative connection 

 between the spectral distribution of energy in black body 

 radiation, and two natural constants which have already been 

 accurately measured, namely the elementary electric charge, 

 and the velocity of light.^ 



Josef Stefan was born in a small village near Klagenfurt in 

 Karnten as son of poor parents of Slav race, who kept a small 

 shop in which they sold food, and were unable to read or 

 write. After he had first been occupied in carrying sacks of 

 flour, it was made possible for him to go to school in Klagen- 

 furt, where he made surprising progress, so that he was then 

 allowed to study at the university in Vienna. After four 

 years of study, the almost uninterrupted succession of his 



1 Further details of this development will be found in any modern text 

 book of Physics. The lay reader may be referred also to C. G. Darwin's 

 The New Conceptions of Matter, London, 1931. The Structure of the 

 Atom, by E. N. da C. Andrade, London, 1927, is a full account for the 

 physicist. 



