Manchester Memoirs, Vol. xlvii. (1903), No. 11. 27 



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 therefore, by most men, regarded as satisfactory. 

 But this is not all of the story. Chemically speaking, the 

 nebulae 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 com- 

 pounds. Here again we have evidence bearing upon our 

 problem, evidence which led me,* more than thirty years 

 ago,' to suggest that the evolution of planets from nebulae 

 had been accompanied by an evolution of the elements 

 themselves. This thought, stated in a reversed 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 growth of the 

 elements ; do we, in the phenomena of radio-activit}% 

 witness their decay ? This is a startling, possibly a rash 

 speculation, but it rests upon evidence which must be 

 considered and weighed. 



We have, then, various lines of convergent testimony, 

 and there are more which I might have cited, all pointing 

 to the conclusion that the chemical atoms are complex, 

 and that elemental matter, in the last analysis, is not of 

 many kinds. That there is but one fundamental sub- 

 stance only, is not proved ; and yet the probability in favour 

 of such an assumption must be conceded. Assuming it 

 to be true, what then is the nature of the Daltonian 

 atom ? 



To the chemist, the simplest answer to this question 

 is that furnished by the researches of J. J. Thomson, to 



"" Evolution and the Spectroscope." Poptilai- Scieirce I\IoJieh/y,]a.n\.ia.xy, 1873. 



