220 Mr. M. Ishino on Velocity of Secondary Cathode Rays 



by experiment, the observed values being much greater than 

 the calculated values. This is explained by supposing that 

 there are some tertiary rays with slow velocities. 



The relative number of the secondary rajs which are 

 emitted with any given velocity can be obtained by finding 

 the differential coefficient of the curves of distribution at that 

 corresponding point. The differential curves are plotted in 

 the figures 5 and 6 in dotted lines. The maximum number 

 of the secondary rays is found at v = 0*7 volt for air, and at 

 v = 0'{) volt for hydrogen. These values cannot be deter- 

 mined very accurately, because the currents at small values 

 of v may be the sum of the secondary and the tertiary rays. 



According to Sir J. J. Thomson's * theory of ionization,, 

 the kinetic energy Q communicated to a corpuscle of mass m x 

 at rest in an atom, by a particle of mass n> 2 moving with 

 velocity V, is given by the equation : 



4?7iim< 



Q = 



()»! + m a ) 2 



e 2 E 2 



i + ni 2 / 



where d is the perpendicular distance from the corpuscle mi 

 to the initial direction of the moving particle m 2 , T is the 

 kinetic energy possessed by the moving particle, and E 

 and e are the charges on the particles m 2 and m 1 respectively. 

 For the case in which the moving particles are the cathode 

 rays, m 1 = m 2 and E = e, and also the equation is simplified 

 as follows : 



T 



1 + -tT 2 



The theory assumes that (1) the force which keeps the 

 corpuscle to the atom is negligible compared with the action 

 of the moving corpuscles, and (2) if the energy communi- 

 cated to a corpuscle in an atom exceeds a certain value, 

 which may be a characteristic for the atom in question, the 

 corpuscle is liberated from the atom. S appose the energy 

 necessary to ionize the atom is q , then the ionization will 

 occur for the values of d less than d given by the relation 



'^-(s^ 1 )* 



* J. J. Thomson, Phil. Mag. xxiii. p. 449 (1912). 



