416 Mr Rutherford, The Discharge of Electrification etc. [Feb. 21, 



travels nearly three times as fast as the air ion in air, and 5 times 

 as fast as the carbonic acid ion in carbonic acid. 



It has been shown that the carriers which are produced under 

 the action of ultra-violet light have very similar properties to 

 the ions which are produced by Rontgen radiation. It is also 

 an interesting result that the velocity of the air ion in Rontgen 

 conduction is not very different from that obtained in ultra-violet 

 light conduction. In a previous paper 1 it has been shown that the 

 sums of the velocities of the positive and negative ions in air, 

 hydrogen and carbonic acid are 3'2, 10'4 and 215 cms. respectively. 

 Assuming for the purpose of comparison that the velocities of the 

 positive and negative ions are equal, the table below shows the 

 relative values of the velocities for the negative ions : 



Considering the widely different methods used for the deter- 

 mination of the velocities in the two cases, the comparative 

 agreement shows that possibly the carrier is the same in the two 

 cases or in any case not greatly different. 



The results obtained in this paper seem to show that the gas 

 near the surface of the negatively electrified plate is ionised under 

 the action of ultra-violet light. The positive ion gives up its 

 charge to the plate and the negative ion is repelled from the 

 plate. This ion travels through air at normal pressure and tem- 

 perature with a velocity of about 1*4 cms. per sec. for a potential 

 gradient of one volt per cm. The velocity of the ion varies in- 

 versely as the pressure and is different for different gases. 



It is intended to continue these investigations on the velocity 

 of the ions and on the general phenomena of ultra-violet light 

 conduction. 



1 Phil. Mag. Nov. 1897. 



Cavendish Laboratory, 

 Feb. 21, 1898. 



