686 Mr. G-. A. Schott on Radiation from Moving Systems 



§27. There appears to be general agreement on the 

 following points : — 



(1) In a vacuum-tube, near the cathode CC, there is a 

 thin layer AA / CC / in which ionization takes place, due 

 to the bombardment by positive ions. 

 B /tc 



//'c 



(2) In the negative glow, beyond BB', ionization takes 

 place, due to cathode rays. 



(3) In the intervening Grookes dark space, BB'AA', 

 there is no ionization, because neither positive ions nor 

 negative electrons have yet acquired the necessary 

 kinetic energy. 



(4) In the negative glow there is a very decided maximum 

 of ionization (proved by H. A. Wilson*). 



(5) The canal-ray particles acquire their velocity in 

 falling through the difference of potential between their 

 place of generation and the cathode. Their velocity is 

 however diminished, by the time they reach the space 

 behind the perforated cathode, by something like 20 to 

 50 per cent., on account of collisions. 



It follows from (3) and (5) that no canal-ray particles are 

 produced at all with velocities between the limits correspond- 

 ing to AA', BB'. The existence of the dark space between 

 the undisplaced and the displaced line seems to indicate that 

 no ions with intermediate velocities are produced by collisions 



o v 



of canal-ray particles with each other or with atoms.* On 

 this view the curve connecting the number of positive ions 

 with the velocity is (n), as shown in the adjoining figure, 



* Wilson, Phil. Mag. [5] vol. xlix. pp. 515-6. 



