S42 HEAT. 



We shall not discuss this subject, but shall refer the reader to Wien's 

 paper already cited for a particular hypothesis by which he obtained as 

 the value of e 



e = 



The work of Lummer and Pringsheim * and others shows that Wien's 

 formula does not agree with experiment through a very wide range of 

 wave-length. 



Planck f by another hypothesis obtains a value 



e = 



which agrees more closely with experiment, f 



It may be noted that if X6 is small compared with c 2 , that is, if the 



C2 



radiation is well on the ultra-violet side of the maximum, e is large and 

 Planck's formula is practically the same as Wien's. If, on the other 



Cl 



hand, Xd is large compared with c 2 , e w - 1 may be put equal to ^ and 

 Planck's formula becomes 



o 



C 2 



or the radiation of a given wave-length well on the ultra-red side of the 

 maximum is proportional to the absolute temperature. 



* Conyres Int. de Phys., ii. p. 41. 



t Deutsch Phys. GeseU., 1900, p. 202; Science Abstracts, iv., No. 507, p. 230. 

 J Kubens and Kurlbaum, Preuss. Ak. Wiss. Herlin, Sitz. Ber. xli. 1900, p. 929; 

 Science Abstracts, iv., No. 371 p. 167. 



