TEE CONSTITUTION OF MATTER 14 1 



similar chemical properties with increasing atomic weight is to be an- 

 ticipated on the general theory that an atom is an electrical structure. 



Evolution of the Elements 



It has long been thought probable that the elements are all built up 

 of some fundamental substance, and Prout's well-known hypothesis that 

 all atoms are composed of hydrogen is one of the best known examples 

 of this idea. The evidence of radioactivity certainly indicates that the 

 heavy radioactive elements are in part composed of helium, for an atom 

 of the latter appears as a result of many of the radioactive trans- 

 formations. No definite evidence, however, has been obtained that 

 hydrogen appears as a result of such transformations ; but as previously 

 pointed out, helium may prove to be an important secondary unit 

 in the structure of heavy atoms. While we have thus undoubted evi- 

 dence of the breaking up of heavy atoms, no indication has yet been 

 observed that the radioactive processes are reversible under ordinary 

 conditions. Many investigations have been made to test whether new 

 elements appear in strong electric discharges in vacuum tubes. While 

 some of the results obtained are difficult of interpretation, no reliable 

 evidence has yet been adduced that one element can be transformed into 

 another under such conditions. 



The question of the evolution of the elements has been attacked 

 from another side. Sir Norman Lockyer and others have suggested 

 that the elements composing the star are in a state of inorganic evolu- 

 tion. In the hottest stars the spectra of hydrogen and helium pre- 

 dominate, but with decreasing temperature, the spectra becomes more 

 complicated and the lines of heavier elements appear. On this view, it 

 is supposed that the light elements combine with decreasing tempera- 

 ture to form the heavier elements. 



There is no doubt that it will prove a very difficult task to bring 

 about the transmutation of matter under ordinary terrestrial conditions. 

 The enormous evolution of energy which accompanies the transforma- 

 tion of radioactive matter affords some indication of the great intensity 

 of the forces that will be required to build up lighter into heavier atoms. 

 On the point of view outlined in these lectures, the building up of a new 

 atom will require the addition to the atomic nucleus of eitber the 

 nucleus of hydrogen or of helium, or a combination of these nuclei. On 

 present data, this is only possible if the hydrogen or helium atom is 

 shot into the atom with such great speed that it passes close to the 

 nucleus. In any case, it presumes there are forces close to the nucleus 

 which are equivalent to forces of attraction for positively charged 

 masses. It is possible that the nucleus of an atom may be altered 

 either by direct collision of the nucleus with very swift electrons or 

 atoms of helium such as are ejected from radioactive matter. There is 



