CONSTITUTION OP MATTER — EUTHEEFOED. 201 



obtained that hydrogen appears as a result of such transformations; 

 -but as previously pointed out on page 191, helium may prove to be an 

 important secondary unit in the structure of heavy atoms. While we 

 have thus undoubted evidence 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 dis- 

 charges 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 con- 

 ditions. 



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 

 evolution. In the hottest stars the spectra of hydrogen and helium 

 predominate, 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 

 temperature 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 condi- 

 tions. The enormous evolution of energy which accompanies the 

 transformation 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 either 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 col- 

 lision of the nucleus with very swift electrons or atoms of helium, 

 such as are ejected from radioactive matter. There is no doubt 

 that under favorable conditions these particles must pass very close 

 to the nucleus, and may either lead to a disruption of the nucleus 

 or to a combination with it. Unfortunately, the chance of such a 

 disruption or combination is so small under experimental conditions 

 that the amount of new matter which is possible of formation within 

 a reasonable time would be exceedingly small and so very difficult 

 of detection by direct methods. Very penetrating X rays or gamma 

 ra3^s may for similar reasons prove to be possible agencies for chang- 

 ing atoms. Although it is difficult to obtain direct evidence, I per- 

 sonally am inclined to believe that all atoms are built up of positive 



