CHAPTER XVII 



RADIO-ACTIVITY AND PHOSPHORESCENCE 



Molecular theory of phosphorescence and of radio-activity — 

 Analogy between phosphorescent molecules and those of 

 radio-active emanation from thorium and radium com- 

 pounds — Model of radio-active and phosphorescent mole- 

 cules — Model of positive ion — The electric theory of 

 matter. 



Molecular Theory of Phosphorescence and of 

 Radio- A ctivity 



Lord Kelvin has shown that the result of 

 repeated collisions between molecules will be to 

 transform their translational energy into energy 

 of higher and higher nodal sub-divisions, and if 

 the molecules, like billiard balls, have a sufl&cient 

 and almost indefinite number of degrees of free- 

 dom, all the energy of translation will become 

 transformed into these higher and higher vibra- 

 tions, so that ultimately in the case of such mole- 

 cules their energy will be radiated away. Fitz- 

 gerald calculated that the air in a room 5 metres 

 cube should lose all its energy in about fifteen 



