66 MORRIS LOEB 



To quote Righi, the neutral chemical atom (as distinguished 

 from the ion) consists of a central mass of positive charge, 

 around which revolve as satellites one or more electro- 

 negative corpuscles, retained in their orbits by some centrip- 

 etal force. 



In connection with this definition, the following points 

 seem to require emphasis: the number of electrons per atom 

 are few, practically corresponding to the valency; this 

 seems to be corroborated by recent experiments of Becquerel 

 on the phosphorescence of uranium minerals at low tempera- 

 tures, which likewise point out that light-emission is not 

 always confined to the negative corpuscle, as Righi would 

 have it. The total mass of the free electrons in an atom is 

 not sufficient to affect the ratio between specific heats for con- 

 stant pressure and constant volume of monatomic vapors, 

 like mercury and cadmium; their velocity in their orbits does 

 not approach that of light, and they have no high momentum 

 retained by comparatively powerful internal attractions. 

 These electrons can not be identical with the X-particles 

 which are projected with terrific force from the uranium, 

 radium and other atoms, according to Rutherford and his 

 followers. 



I need only touch briefly on the electric discharges in vac- 

 uum tubes: it is generally accepted that we distinguish 

 Lenard or cathode rays, which are negative, and positive 

 Goldstein or canal rays within the tube. They can be de- 

 flected by electric or magnetic fields, they produce mechani- 

 cal and heating effects, cast visible shadows, etc., and they 

 behave in general like streams of actual particles charged 

 with electricity. When the cathode ray strikes an impene- 

 trable obstacle, like glass, the X-rays are produced as a sec- 

 ondary effect: these do not behave as if conveyed by neutral 

 particles; have vast penetrating power; contain no electric 



