CHAPTER XVIII. 



SUMMARY OF OTHER CONSEQUENCES OF ELECTRON 



THEORY. 



Radio-activity. 



IF many atoms of a substance have electrons attached 

 to them, and if these are performing orbital revolutions; 

 it is natural to ask how then can it be that substances 

 are not constantly emitting waves and radiating away 

 their energy. For we have seen in Chap. X. 

 that electric charges in revolution or vibration 

 constitute radiators, and must emit more or less 

 radiation ; thereby dissipating their kinetic energy 

 and gradually either coming to rest or effecting 

 some other change. Fortunately, owing to the 

 brilliant researches of Becquerel, Curie, and others, 

 certain substances have been found in which the 

 radiation intensity reaches a very perceptible mag- 

 nitude ; and it appears that this radiation may 

 be of several kinds 



1st, of waves or pulses analogous to Rontgen 

 radiation : called 7 rays ; 



2nd, of rays analogous to cathode rays consist- 

 ing of electrons bodily shot off: called ft 

 rays; 



3rd, of positively charged ions or atoms, or 



