JILY 10. lIXKi. 



SCIENCE. 



47 



It has been thought, for example, that radio- 

 active substauees may have the power of 

 absorbiug the energy of certain rays, hith- 

 erto undetected, which are all the while 

 proceeding through space, coming perhaps 

 from the sun. The radioactive substances 

 might utilize the energy thus absorbed in 

 the development of Beccpierel rays, just as 

 tluoreseent substances utilize the energy 

 absorbed from sunlight in producing lu- 

 minescent phenomena. This view, I be- 

 lieve, is .suppoi-ted by the Curies. Sir 

 Wm. Crookes has suggested that radio- 

 active substances possess the power of 

 utilizing the energy of surrounding bodies. 

 Such an explanation might possibly con- 

 tradict the second law of thermodynamics; 

 yet, since the process is not a cyclic one, 

 I do not believe that any contradiction 

 would be found. An objection to this ex- 

 jtlanation has been raised, based on the fact 

 that radioactivity continues when the sub- 

 stance is placed in a vacuum. Crookes 

 replies, however, that the best vacTium ever 

 obtained contains millions of molecules per 

 cubic centimeter, so that enough are left 

 to supply the energy needed. A test might 

 be applied, as suggested by J. J. Thomson, 

 by placing the active substance in an ice 

 calorimeter entirely surrounded by ice. If 

 the ice melts, as is probable, it would seem 

 that the Crookes explanation could not 

 hold. 



Elster and Geitel suggested, a few years 

 ago, that the energy might be derived from 

 processes of molecular or atomic change 

 which accompany the development of 

 Becquerel rays. According to this view, 

 an active substance is one which is slowly 

 changing from an unstable condition into 

 a more permanent form ; the processes 

 which go on during this change may bring 

 about the development of Beequerel rays, 

 while the energy developed is that liber- 

 ated dvu'ing the transition. The produc- 



tion of Th-X from Th is perhaps the first 

 stage in such a change; the decay in the 

 activity of the Th-X and the production 

 of the emanation, perhaps form the second 

 stage ; while a third step in the progressive 

 alteration of the original substance is 

 shown by the development of excited ac- 

 tivity from the emanation. The final 

 products of this disintegration process are 

 doubtless much simpler in their structure 

 than the original substance, and are prob- 

 ably not radioactive. It has been sug- 

 gested that helium, which has so far been 

 obtained only from radioactive minerals, 

 may be one of the final products of radio- 

 active change. 



Perhaps the most serious diflBeulty in 

 accepting the explanation just mentioned 

 arises from the large quantities of energy 

 involved. It seems abiiost incredible that 

 so much energj' could be stored in a few 

 milligrams of material. The changes as- 

 sumed are, however, atomic changes. i\Iay 

 it not be that .such changes involve energy 

 quantities of a higher order? As we pro- 

 ceed from the ordinary motions of mass 

 mechanics toward motions of a finer grain 

 the energ>' involved increases. A falling 

 raindrop posses.ses energy due to its mass 

 motion ; the energy liberated when it 

 freezes is much greater ; and the energy 

 involved in the formation of the drop from 

 oxygen and hydrogen is greater still. May 

 not the energy of atomic synthesis and dis- 

 integration be as nuieh greater than that 

 of ordinary chemical change as the latter 

 is greater than the energy of physical 

 change ? The view advanced by Elster and 

 (icitel appears to me to give the best ex- 

 planation that has yet been offered. But 

 this question of the energy of the rays, 

 like many other questions that have been 

 raised by the study of radioactivity, can by 

 no means be lookeil upon as .settled. 



Ernest ^Ierritt, 



