430 Sir J. J. Thomson on the Origin of 



The series may be represented as 



(l) U-S. = (-!(-„- -.), 



x 7 \)tr 117 



:s) 



(4) u-s. = cf / -*--,)> 



Vf/zj + 'O)- nv 



where L s and L c may have different values corresponding to 

 -different positions of the magnetic boundary. 



We see from this that the difference in the frequencies of 

 two lines in a series of types (1) or (3) will be the frequency 

 of a line in another series of the same type. 



The differences between the frequencies of any two lines 

 in a series of type (2) will be the frequency of a line in 

 another series of type (3). 



The difference between the frequencies of any two lines 

 in a series of type (4) will be the frequency of a line in 

 another series of type (1). 



Thus, if we take the lines belonging to any one series, the 

 complete spectrum of the gas will contain a line whose 

 frequency is the difference of the frequencies of the two 

 lines in the series. 



It must be remembered that the two lines must be selected 

 from the same series, if the two lines are selected at random 

 from the spectrum there need not be a line whose frequency 

 is the difference in frequency of the two lines. 



Planck's Law. 



The view that the vibrations which give rise to radiation 

 are determined by the magnetic forces, leads, if we assume a 

 simple relation between the electric and magnetic forces, to 

 Planck's law, and gives a physical concept for the Quantum 

 Theory. 



For suppose that an electric field is accompanied by a 

 magnetic one, the magnetic induction B being in the direc- 

 tion of the electric force R and connected with it by the 

 relation 



