i82 PHYSICAL SCIENCE 



immediately coagulated the globulin. On the 

 other hand, the /5 and 7 rays were found to 

 induce certain chemical reactions, liberating iodine 

 from iodoformin presence of oxygen. This change 

 is also produced by ordinary light and by Rontgen 

 rays, but not by the a radiation. These results, 

 physical and chemical, may explain some of 

 the curious physiological effects of radio-active 

 substances. 



It seems unlikely that radio-activity will ever 

 be cheap enough for us to use its energy to develop 

 mechanical power, but it is just possible that the 

 phosphorescence of sensitive screens in the neigh- 

 bourhood of a radio-active body may some day 

 be employed as an effective source of light. I n this 

 way luminous effects would be obtained directly 

 from a store of energy self-contained and practi- 

 cally inexhaustible, whereas, in all our present 

 arrangements, light is derived from a hot body, 

 and large quantities of energy are necessarily 

 wasted in maintaining the incandescence. 



In order to gain some insight into the cause of 

 radio-activity, we must now examine another series 

 of phenomena of fundamental importance, which 

 were discovered in the case of uranium by Crookes 

 and by Becquerel, and in the case of thorium by 

 Rutherford and Soddy. By definite processes of 

 chemical fractionisation, somewhat like those by 

 which radium was isolated from pitch-blende, pro- 

 ducts can be obtained in minute quantities from 

 uranium and thorium many times more active than 

 those substances themselves. The uranium and 

 thorium from which those products have been 

 separated lose much of their activity ; the radiation 



