232 CHEMISTRY 



instability which is difficult to explain. Radium gives off material 

 emanations that are different from itself; they are gaseous and inert; 

 in them the spectrum of helium has been observed. From one element 

 another seems to be derived, and all our notions of what an element 

 should be are thrown into temporary confusion. I say "temporary," 

 for I believe that order will be restored, and that a deeper insight 

 into the constitution of matter is close at hand. 



Pardon me now if I seem to wander from one part of my subject to 

 another. Between the various departments of knowledge there are 

 no sharp boundaries, and the solution of a problem often depends 

 upon the convergence of testimony from many different directions. 

 The nature of the elements is primarily a question for the inorganic 

 chemist; but physics has much to say upon the subject, and even the 

 serial relations of organic compounds offer suggestive analogies which 

 are entitled to some consideration. The periodic system, with its 

 fulfilled prophecies, tells us that the elements are related one to 

 another by some distinct law; the spectroscope gives us evidence of 

 a different order; electrical phenomena have their share in the story, 

 and the modern phenomena of radioactivity offer the latest testi- 

 mony of all. What conclusions seem to be foreshadowed by the data 

 now in hand? 



One of the earliest achievements of the spectroscope was the 

 rehabilitation of the nebular hypothesis. The resolution of some 

 nebulae into clusters of stars had shaken faith in Laplace's specu- 

 lation; but when it was proved that others were really clouds of 

 incandescent gas, belief in the hypothesis was restored. One point, 

 however, was of peculiar interest: in the nebulae only one or two 

 elements, low in the scale of atomic weights, could be seen; in the 

 whiter and hotter stars a few more substances appeared; colored 

 stars were of still greater complexity, and so on progressively from 

 the simplest constitution to the material heterogeneity of our globe. 

 If suns and planets were evolved from nebulae, it seemed as if the 

 chemical elements had been successively generated at the same time 

 a supposition which was certainly legitimate, although it was at 

 first denied by some chemists as unworthy to be heard. At all events, 

 here was testimony bearing upon the problem of the elements, 

 although its full significance was not so clear. It could be pigeon- 

 holed, but not thrown away. 



Recently, and in great part through the researches of J. J. Thom- 

 son, evidence has been obtained of the reverse order. On one side an 

 evolution of the elements is apparently indicated; Thomson's experi- 

 ments suggest a breaking-down. By studying the ionization of gases, 

 phenomena were observed which point to the existence of particles 

 smaller than the Daltonian atoms, and a beginning has been made 

 toward the identification of matter with electricity. The negative 



