at the Electrodes in Vacuum-Tube Discharge. 628 



under the influence o£ Rontgen rays, the drop at the electrode 

 is reduced when the rays play upon its discharging surface *. 



The phenomena seem to indicate that, to give up its charge 

 to the electrode, the ion in gases must first be brought to 

 rest. The fact that cathode rays may be reflected from a 

 metallic surface f shows that the negative ion does not dis- 

 charge in the time (or condition) of elastic impact. The 

 experiments of Cady on their heating effect J prove that 

 cathode rays give up their kinetic energy with their charge. 

 These observations furnish direct evidence that the velocity of 

 impact tends to prevent the discharge of the ions. 



If then, the ion must come to rest before giving up its 

 charge, unless the electric force at the electrodes be as great 

 as the force of elastic reaction it will vibrate back and forth, 

 giving up its kinetic energy in setting the molecules of the 

 gas and the electrode in a state of greater agitation, that is, 

 in raising the temperature of both. By increasing the number 

 of molecules of gas in a given volume we should expect to 

 facilitate the discharge, in that by increasing the number of 

 collisions in a given time the ion will more quickly reach 

 that state which, in reference to an electric current, is looked 

 upon as a zero-velocity. We have, in this conception of the 

 discharge, the ion giving up its kinetic energy acquired in 

 the electric field, in imparting by impact increased velocity 

 to the surrounding molecules, the same being evidenced 

 as heat. 



Variation in Drop at the Electrodes with Current and 

 Gas-presswe. 



It is important to know the variation in the drop at the 

 electrodes with the velocity of impact of the discharging ions. 

 For the same gas it would be expected that the velocity of 

 the ions would vary with the current. Though we cannot, 

 without a further knowledge of the number of ions in motion, 

 gain from the magnitude of the current a definite knowledge 

 of the velocity of the ions, yet, in lieu of direct measurements, 

 some interesting relations between the drop at the electrodes, 

 current, and gas-pressure have been observed. 



At the Anode. — Other conditions remaining constant, the 

 drop at the anode (for disk-electrodes) is, as found by the 

 writer §, at least with moderate current-densities, constant. 

 The velocity of the negative ions as they arrive at the anode 



* C. D. Child, Wied. Ann. lxv. p. 152 (1898). 

 t H. Starke, Wied. Ann. lxvi. p. 49 (1899). 

 % W. Cady, Ann. d. Phys. i. p. 678 (1900). 

 § Wied. Ann. lxviii. p. 752 (1899). 



