98 UNIVERSITY OF MISSOURI BULLETIN 



sion of the a rays and the emanation in the case of radio- 

 active substances. 



The general experimental evidence indicates further that 

 the corpuscles play two distinct roles in the structure of the 

 atom, one as lightly attached and easily removable satellites 

 or outliers of the atomic system, and the other as integral 

 constituents of the interior structure of the atom. The former, 

 which can be easily detached or set in vibration, probably 

 play an important part in the combination of atoms to form 

 molecules, and in the spectra of the elements ; the latter, which 

 are held in place by much stronger forces, can only be re- 

 leased as a result of an atomic explosion involving the disin- 

 tegration of the atom. For example, the release of a cor- 

 puscle with slow velocity by ordinary laboratory agencies does 

 not appear to endanger the stability of the atom, but the 

 expulsion of a high-speed corpuscle from a radio-active sub- 

 stance accompanies the destruction of the atom. 



The atom with its detachable electrons is sometimes com- 

 pared to the solar system. The analogy is somewhat far- 

 reaching. Fournier d'Albe makes the following comparison. 



If the solar system is an atom on a large scale, the sun 

 must be regarded as the positive nucleus, and the planets as 

 the electrons. It is actually found that the sun has a positive 

 charge and the earth a negative charge. But these charges 

 are comparatively infinitesimal, and do not perceptibly influ- 

 ence the force between them. In this point the analogy fails. 

 On the other hand, the ratio of the masses is striking. That 

 of Jupiter is about ■— that of the sun, and approaches 

 the mass of an electron compared with a hydrogen atom. The 



mass of the earth is -^-^ that of sun, and this ratio is 

 roughly the same as that of an electron to the atoms of the 

 heavy metals. It may be said that in the solar system there 

 are examples of the various actual ratios of masses between 

 an electron and its positive nucleus, though in the case of 



