Structure of the Atom. 261 



On the other hand, the absorption of a very small amount, 



1 Ae 



JlW-^n) 2 ) of energy in the form of radiation of 



frequency v n , will liberate the electron, and cause the re- 

 conversion of its potential energy into the kinetic energy 

 with which it escapes from the atom. Thus we obtain a 

 complete explanation of the readiness with which iveak ultra- 

 violet light or Ronfgen radiation can liberate electrons posses- 

 sing the quantum of energy. The quantum is not absorbed 

 from the radiation, it is absorbed from the energy of the 

 electron wben it enters the atom and is stored for future 

 use. 



Using Whiddington's result that the kinetic energy of a 

 cathode particle, exciting the hardest Rontgen radiation in 

 an atom of atomic weight -57, cannot be less than ^I0 l<5 ?z 2 m, 

 we get 



\ 10 1( W 2 m > hv. 



Hence v < 6*77 (10) 14 , the actual value being 8'2 (10) 14 . 

 In the case of a helium atom we find v <£ 1*08 (10) 16 . 



As in Professor Thomsons investigation, the energy of 

 the pulse radiation is proportional to the square of the 

 frequency in consequence of repulsion effectively inversely 

 proportional to the cube of the distance, which is in ac- 

 cordance with observation. Tbat law of repulsion also leads 

 to a formula for the distribution of energy in the spectrum, 

 which has been shown to possess some correspondence with 

 fact (Sir J. J. Thomson, Phil. Mag. July 1910). 



A similar construction can be imagined with any desired 

 law of repulsion. In particular the law of repulsion requisite 

 in order to give Planck's law for pulse radiation may readily 

 be expressed by an infinite series. If Fi(r) be the law of 

 repulsion, while F 2 (r) is the law of attraction which is 

 superposed upon it in the thin shells of thickness r»"— *•»', 

 we have 



F 2 ' (HO e = F/ (r n ) e + l*K? Q 2 - AY , 



where pi and p n are the constants of, say, the lines in Palmer's 

 series, C being an absolute constant. 



§ 3. An Atom characterized by axial Rotation. 



In the preceding case, when the collisions are seldom, the 

 spectrum is practically a line or band spectrum. The con- 

 tinuous radiation In the region of very great wave-length 



