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SCIENCE. 



[N. S. VOL.XVIII. No. 460. 



and it is of course possible that they may 

 not be finally sustained. Their value to us 

 at the present moment lies in their sug- 

 gestiveness, and in the curious way in 

 which they reinforce other arguments of 

 similar purport. The possibility that the 

 chemical atoms can be actually broken 

 down into smaller particles of one and the 

 same kind, is, to say the least, startling, 

 but it can not be disregarded. The evi- 

 dence obtained by Thomson is, so far as it 

 goes, positive, and it is entitled to receive 

 due weight in all discussions of our present 

 problem. It is the first direct testimony 

 that we have been able to obtain, all pre- 

 vious evidence being either negative or cir- 

 cumstantial. It may be misinterpreted, 

 but it is not to be pushed aside. 



In direct line with the inferences of 

 Thomson 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 concern- 

 ing it must be held open to revision, 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 con- 

 clude that from this element a new body 

 is continiially generated, in which the radio- 

 activity steadily decays. This loss of em- 

 anative power is in some sort of equilibriiun 

 with the rate of its formation. When tho- 

 rium is 'de-emanated,' it slowly regains, its 

 emanative power. The eraanation is a 

 'chemically inert gas, analogous in nature 

 to the members of the argon family.' The 

 final conclusion is that radio-activity may 

 be 'considered as a manifestation of sub- 

 atomic chemical change.' This word 'sub- 

 atomic' is one of ominous import. It im- 

 plies atomic complexity, and it also sug- 

 gests something more. The property of 

 radio-activity is most strikingly exhibited 



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



by the metals radium, thorium and uran- 

 ium; and these have the highest atomic 

 weights of any elements known. If the 

 elements are complex, these are the most 

 complex, and therefore, presmnably, the 

 most unstable. Are they in the act of 

 breaking down? Is there a degradation of 

 matter comparable with the dissipation of 

 energy? We can ask these questions, but 

 we may have to wait long for a reply. 

 There is, however, another side to the 

 shield, and the universe gives us glimpses 

 of a generative process, an elementary evo- 

 lution. 



The truth or falsity of the nebular hy- 

 pothesis is still an open question. It is 

 a plausible hypothesis, however, and com- 

 mands many strong arguments in its favor. 

 We can see the nebulffi, and prove them to 

 be clouds of incandescent gas; we can 

 trace a progressive development of suns and 

 systems, and at the end of the series we have 

 the habitable planet upon which we dwell. 

 The nebular hypothesis accounts for the 

 observed condition of things, and is there- 

 fore, by most men, regarded as satisfactory. 

 But this is not all of the story. Chemically 

 speaking, the nebulfe are exceedingly simple 

 in composition; the whiter and hotter 

 stars are a little more complex ; then come 

 stars like our sun and finally the finished 

 planets with their many chemical elements 

 and their myriads of compounds. Here 

 again we have evidence bearing upon our 

 problem, evidence which led me,* more than 

 thirty years ago, to suggest that the evolu- 

 tion of planets from nebulte had been ac- 

 companied by an evolution of the elements 

 themselves. This thought, stated in a re- 

 versed form, has since been developed and 

 amplified by Lockyer, and it is doubtless 

 familiar to you all. In the development of 

 the heavenly bodies we seem to see the 



* ' Evolution and the Spectroscope.' Popular Sci- 

 ence Monthly, Janxiary, 1873. 



