INTRA-ATOMIC ENERGY. 285 



darkness. How, indeed, was it possible to suppose that they could 

 evolve'^ Was it not universally admitted that they were indestructi- 

 ble? Everything was changing in the Avorld, and ever3"thing was 

 ephemeral. Beings succeeded each other, always taking on new forms; 

 stars ended 1)}' becoming extinguished; the atom alone was not sub- 

 jected to the action of time, and seemed eternal. The doctrine of its 

 immutability reigned for two thousand years, and nothing- seemed to 

 indicate that it could ever ])e shaken. 



We have detailed the experiments which resulted in the crumbling 

 away of this aiiticjue belit^f. We know now that matter disappears 

 slowl}' and that the atoms which compose it are not destined to last 

 forever. 



If, however, atoms are condemned to a relatively ephemeral exist- 

 ence, it is natural to suppose that they were not formerly what they 

 are to-day and that they must have evolved during the course of 

 ages. What were they formerly? Through what successixe phases 

 have they passed? What gradations of form have they assumed? 

 What were formerly the various material substances which now sur- 

 round us — stone, lead, iron; in a word, all bodies? 



Astronomy alone can answer, in some degree, such questions; and, 

 indeed, it has done so. Knowing how to penetrate by spectral analysis 

 into the structure of stars of various ages that illuminate our nights, 

 it has been able to show us the transformations that matter undergoes 

 at its earliest stages. 



The eminent astronomer, Sir Norman Lock3"er, director of one of 

 the large English observatories, first showed this evolution of matter 

 in the stars, and was also the first who dared to maintain that the atoms 

 of elementary bodies were dissociable." 



The proofs that he furnished of this last assertion were convincing-, 

 but minds were not then prepared for them, and it was necessary to 

 wait till the discovery of the cathedic radiations and the radio-activity 

 of matter before the antique doctrine of the indestructibility of atoms 

 could be shaken. 



The point of departure of the researches of Sir Norman Lockyer 

 was this fundamental fact that, contrary to the ideas that first prevailed, 

 the spectrum of each chemical element varies according to the temper- 

 ature to which the element is submitted. For exampl(\ the spectrum 

 of iron in an ordinary flame is quite different from the spectrum of 

 the metal in the electric arc. In the flame it presents only a small 

 numl)er of lines. In the arc it presents nearl}^ 2,000 of them. The 

 spectrum of the same metal likewise varies according as we observe it 

 in the hottest or the less hot portions of the sun. In tubes containing 



«The researches pursued by Sir Norman Lockyer durinjj; twenty-five years liave 

 been jiul)lislie<l liy liiin in a recent liouk, Inorganic P'vohifidii, London, li'OO. 



