of Electrons to the Theory of Phosphorescence. G25 



a certain quantity of electrons, if the velocity of these latter 

 permits it. 



As the luminophorous system is to a certain extent 

 electronogenous, it will, when acted upon by light, send 

 back electrons into the surrounding space. I£ the quantity 

 of electrons absorbed is greater than the quantity emitted, 

 the value E m , the critical value of the luminophorous system, 

 will be attained after a certain time, and the luminophorous 

 system will produce its own particular light. 



The luminophorous system is not able to absorb electrons 

 indefinitely. When the condition of equilibrium is destroyed 

 the system will send back a number of electrons.; the magni- 

 tude of the number depending upon the energy the system 

 received from the electrons which came toit. Thus a stationary 

 condition is established. The internal energy corresponding 

 to the stationary condition will be equal to E + C. The value 

 of the constant C depends upon the quality and quantity of 

 the secondary rays that traverse the luminophorous system, 

 as also on the surrounding medium and on the temperature. 



Let us consider the moment at which the production of 

 secondary rays ceases, and at this moment let us put £ = 0. 



From this moment on the internal energy E of the lumino- 

 phorous system will decrease and ' we may admit, in a first 

 approximation, 



_dE 

 dt 



= «E-E , 



whence 



E=E + (>-"'. 



The values of Ci and of a. are functions of the properties of 

 the luminophorous system, of the surrounding medium, and 

 of the temperature. 



The intensity of the phosphorescence may be expressed, in 

 a first approximation, as 



I=c(E-E ro ), 



whence we get 



A=C lC , 



B = c(E m -E ). 



This formula, which gives us a relation between the intensity 

 of the phosphorescence and the time, is in agreement with the 

 recent experiments of Nichols and Merritt on sidotblende. 



IY. — As I said, the constants A and B are functions of 

 the temperature. A and B diminish with an increase of tem- 

 perature. Consequently it follows that there will be a certain 



Phil. Mag. S. 6. Yol. 13. No. 77. May 1907. 2 U 



