122 KADIOACTIVITY. 



processes we so far have had no conception of and in which a mil- 

 lion times greater amount of energy is set free than any we have as 

 yet been in a position to investigate. 



Some time ago a happy combination of circumstances relieved us 

 of this painful uncertainty. Observations in various fields — in 

 optics, electricity, and radioactivity — have worked together to point 

 out what these processes might be, and we have been fortunate enough 

 to observe directly such an illustration. 



All the processes hitherto known to us may be described as molecu- 

 lar ; our chemistry is a chemistry of the molecule. We have investi- 

 gated how the molecule may be built up out of the atom of the 

 chemical elements or may be disintegrated into atoms again, and we 

 have learned to measure the energy thus transformed. The chemical 

 elements and their atoms have hitherto been for us the completed, 

 the fixed, building stones which all science has tried in vain to trans- 

 form. But now we believe that we have advanced a step farther, and 

 are able to show that the elements are not unchangeable, the atoms 

 not indivisible. 



It was unquestionably one of the greatest strides forward in the 

 domain of physics and chemistry when the fruitless speculations and 

 senseless experiments of the alchemist were brought to an end by the 

 ever-strengthening theory that the universe was built up of atoms, 

 of a limited number of simple, unchangeable, chemical elements. 

 The brilliant developments and great achievements of chemistry were 

 not less adapted to support this theory than the previous but always 

 fruitless attempts to disintegrate the chemical elements, to divide the 

 atom. 



On the other hand, one may not now assert that the separate ele- 

 ments stand unrelated to each other, but must rather acknowledge 

 their interdependence. The most striking demonstration of this is 

 the periodic system of the elements formulated by Lothar Meyer and 

 Mindeljeff, which clearly shows that the properties of the elements 

 are periodic functions of their atomic weight. When observing, for 

 example, the group Li, Na, K, Rb, Cs, elements of remarkably similar 

 characteristics, is it not surprising that I have the atomic weight of 

 each succeeding one in the column if I add 1X16 or 3X16 to the pre- 

 ceding? That this is the confirmation of a law and not a chance 

 play with figures is proved by the fact that Mindeljeff, because of the 

 gaps in his tables, prophesied that such and such elements, with cer- 

 tain characteristics, would be found, and they were found — gallium, 

 scandium, germanium — exactly as he had foretold. What is the sig- 

 nificance, then, of the 1X16 and the 3X16 in the above example? 

 Would that I could solve that, but it is beyond my power. 



Every chemical element gives out, like a glowing vapor, a spectrum 

 in which the colors are not continuous and merged into each other 



