of Electrons to the Theory of Phosphorescence. 623 



belonging to an atom, begins to produce light as soon as its 

 internal energy exceeds a certain minimum, which Prof. J. J. 

 Thomson calls the critical value. This value may be reached 

 either by raising the temperature (which method, however, 

 is not very efficient) or bv increasing the number of electrons 

 of the system of corpuscules. 



If the luminosity of a system of corpuscules is brought about 

 by increasing the number of electrons, this system will 

 remain luminous as long as its energy does not fall beneath 

 the critical value. This diminution may arise from the 

 following causes : — (1) Diminution of the energy by radiation. 

 (2) Expulsion of the electrons of the system. (3) By the 

 formation of a new confio-uration of the electrons in the 

 interior of the system. 



I suppose the existence in every phosphorescent or fluor- 

 escent body of two kinds of systems of corpuscules, endowed 

 with different properties, and intimately united. To denote 

 these systems I will use the terms elect ronogenous system and 

 lumihophorous system. 



An electronogenous system has the power of shooting out 

 electrons when -acted upon by light. Nearly all bodies con- 

 tain electronogenous systems, as is proved by experiments 

 made on the secondary rays produced on the surface of bodies. 

 Moreover, the experiments of Lenard, Elster and Geitel. 

 Ramsay and Spencer, Sagnac, and others demonstrate that 

 the quantity of electrons emitted under the action of light, 

 varies considerably with different bodies and with the qualitv 

 of the light employed, The velocity of the electrons shot 

 out varies likewise. TVe are thus forced to admit that the 

 systems of corpuscules are electronogenous in different 

 degrees. 



A luminophorons system is a system of corpuscules whose 

 internal energy is very near the critical value. Hence the 

 absorption by it of even a relatively small quantity of 

 electrons is sufficient to make it luminous. In certain cases 

 it will be able to absorb a quantity of electrons such that 

 its internal energy considerably surpasses the critical value 

 of Prof. J. J. Thomson. It is certain that a luminophorous 

 system will absorb those electrons that traverse it only if the 

 velocity of these latter bears a certain relation to its own 

 internal energy and structure. 



Every luminophorous system may, to a certain extent, be 

 also electronogenous. 



Every atom may include one or several luminophorous 

 systems, but every luminophorous system produces only one 

 kind of light having its own characteristic spectrum. 



