26 Clarke, TJic Atomic Theory. 



In direct line with the inferences of Thomscjn are the 

 results obtained by Rutherford and Soddy in their 

 researches upon radio-activity. Here, again, we have a 

 subject so new that all opinions concerning it must be 

 held open to revisiori, but so far as we have yet gone the 

 evidence seems to point in one way. Rutherford and 

 Soddy* have studied especially the emanations given off 

 by thorium, and conclude that from this element a new- 

 body is continually generated, in which the radio-activity 

 steadily decays. This loss of emanative power is in some 

 sort of equilibrium with the rate of its formation. When 

 thorium is " de-emanated," it slowly regains its emanative 

 power. The emanation is a "chemicall}' inert gas, 

 analogous in nature to the members of the argon family." 

 The final conclusion is, that radio-activity may be " con- 

 sidered as a manifestation of sub-atomic chemical change." 

 This word " sub-atomic " is one of ominous import. It 

 implies atomic complexity, and it also suggests something 

 more. The propert}- of radio-activity is most strikingly 

 exhibited by the metals radium, thorium and uranium ; 

 and these have the highest atomic weights of any ele- 

 ments known. If the elements are complex, these are 

 the most complex, and therefore, presumably, the most 

 unstable. Are they in the act of breaking down ? Is 

 there a degradation of matter comparable with the dis- 

 sipation of energy ? We can ask these questions, but we 

 may have to wait long for a reply. There is, nowever, 

 another side to the shield ; and the universe gives us 

 glimpses of a generative process, an elementary evolution. 



The truth or falsity of the nebular hypothesis is still 

 an open question. It is a plausible hypothesis, however, 

 and commands many strong arguments in its favour. 

 We can see the nebulae, and prove them to be clouds of 



'Phil. Mag.. (6) 4 pp. 395, and 581. 



