66 Prof. Max Planck : New Paths 



of the wind, the waves will be maintained for some time and 

 will pass from one shore to the other. But there will be a 

 certain characteristic change in them. During their impact 

 on the shore, or on other solid obstacles, the energy of 

 motion of the longer and coarser waves is converted to an 

 ever greater extent into the energy of motion of shorter and 

 slighter waves ; and this process will continue until at last 

 the waves have become so small and their motion so slight 

 that they are quite lost to view. That is the familiar 

 transmutation of visible motion into heat, of molar into 

 molecular, of ordered into disordered motion ; for in ordered 

 motion many neighbouring molecules have a common 

 velocity, whilst in disordered motion every molecule has its 

 separate and separately directed velocity. 



This process of disintegration or subdivision does not 

 proceed indefinitely, but finds its natural limit in the size 

 of the atoms. For the motion of a single atom by itself is 

 always an ordered one, since the separate parts of an atom 

 all move with the same common velocity. The larger the 

 atoms, the less can the total energy of motion be subdivided. 

 So far, everything is perfectly clear, and the Classical 

 Theory is in excellent agreement with experience. 



But now let us take another and quite analogous process, 

 not dealing with water waves but with waves of light and 

 heat. Let us assume that rays emitted by a brightly glowing- 

 body are collected by suitable mirrors into a completely 

 enclosed hollow space, and that they are continually thrown 

 to and fro between the reflecting walls of that space. Here 

 also there will be a gradual transmutation of the energy of 

 radiation from longer waves to shorter waves, from ordered 

 radiation to disordered radiation. The longer and coarser 

 waves correspond to the infra-red rays, and the shorter and 

 slighter waves correspond to the ultra-violet rays of the 

 spectrum. Hence, according to the Classical Theory, we 

 must expect the total energy of radiation to concentrate 

 itself upon the ultra-violet portion of the spectrum ; or, in 

 other words, we must expect the infra-red and the visible 

 rays to disappear gradually and convert themselves ulti- 

 mately into invisible ultra-violet or chemical rays. 



But of such a phenomenon no trace can be discovered in 

 Nature. The conversion sooner or later attains a perfectly 

 definite and assignable limit, and after that, the radiation- 

 conditions remain stable in every respect. 



In order to reconcile this fact with the Classical Theory 

 the most varied experiments have already been made, but 

 the result has always been that the contradiction went too 



