ELECTRONIC MAGNITUDES 313 



that this charge is uniformly distributed over a sphere, 

 the radius of the electron is indicated as about 2X10~ 13 

 cm. Such magnitudes are quite beyond our compre- 

 hension except by analogies, such as a statement of 

 how long it would take if every man in the world should 

 count before the total number counted equaled the 

 number of electrons equivalent in inertia to one gram. 

 They may be more nearly visualized after consider- 

 ing some phenomena of ionization of gases. 



For experiments involving ionization X-rays may be 

 used (cf. page 190) or the gas may be exposed to a 

 radioactive substance. The radiations from the latter 

 are of three types, although all three do not usually 

 occur in the case of a single substance. They are 

 usually designated by alpha, beta, and gamma re- 

 spectively. In this case also the terms " radiation " 

 and "rays" are misnomers, at least as far as concerns 

 the first two, for the a rays are formed of a stream of 

 positively charged helium atoms and the ft rays by 

 electrons. The 7 rays are really a radiation, being a 

 penetrating radiation of the nature of a pulse like the 

 X-rays. 



The disintegration of an atom of radium, for example, 

 results in the projection in opposite directions of a 

 helium atom (deficient by one electron) and a niton 

 atom, with velocities inversely as the masses. The 

 lighter a particles have about 100 times the greater 

 velocity, and travel about seven tenths as fast as does 

 light. The niton atoms, themselves, disintegrate 

 further and after successive changes in which further 

 a particles are lost, as well as electrons, a more stable 

 resultant of polonium is reached. 



