in the Solar Chromosphere, 477 



quantity of energy liberated in the process. The quantity 

 considered is 1 gm. atom. 



The value of U in the case of alkaline earths, and many 

 other elements, can easily be calculated from the value of 

 the ionization potential of elements as determined by Franck 

 and Hertz, MacLennan *, and others. Let V = ionization 

 potential. Then, to detach one electron from the atomic 

 system, we must add to each atom an amount of energy 

 equivalent to that acquired by an electron falling through a 

 potential difference V, where V (in volts) is given by the 

 quantum relation, 



eV_ 

 300 



=hv , (3) 



v being the convergence frequency of the principal series, 

 i. e., (1, s) in Paschen's notation j\ If this quantity be 

 multiplied by the Avogadro number N, and expressed in 

 calories, we obtain U. 



Thus if V = l volt, we have 



TT *V.N 9645. 10 8 9 ono ia4 i • 



U = 77300 = 4^W = 2 ' 302 ' 10 caWs - 



Table III. contains for future use the values of the 

 ionization potentials J as far as known, and the calculated 



Table III. 



Ionization 



Element. Potential. 



Mg 765 



Ca 612 



Sr 5-7 



Ba 512 



Ra ? 



Na 5112 



K 4-318 



Rb 4155 



Cs 3873 



Zn 9-4 



Cd 9 



Hg 10-45 



U in Calories. 



1-761 . 



10 5 



1-409 



,, 



1-313 



,, 



1-178 



,, 



? 





1177 X 



10' 



•994 



,, 



•957 



>> 



•892 



>> 



2-164X 



:io 5 



2-072 



M 



2-406 



>> 



* MacLennan, ' Proceedings of the Physical Society of London,' Dec. 

 1918. 



t Paschen uses the symbol (1*6, *), but following Sommerfeld (loc. cit. 

 p. 243), I have taken off -5 and used (1, s). 



\ MacLenuan, loc. cit. p. 18. 



