of Gases exposed to Rontgen Rays, 249 



air, while the velocity of the hydrogen ion was much greater 

 than that of air. The experiments on the amount of electri- 

 fication with variation of E.M.F. and velocity of the blast 

 confirm the previous results which were obtained in an entirely 

 different way. 



Velocity of the Ions. — An approximate determination of the 

 velocity of the conducting particles for air can be made by de- 

 termining the rate of leak of a charged wire connected to an 

 electrometer when air is blown at varying velocities from a tube 

 of known diameter along the charged wire. If we assume the 

 current of air of high velocity from the tube to be confined 

 within narrow limits for a short distance from the orifice, the 

 velocity of the ions in order that a known proportion of the 

 ions should reach the electrode can easily be deduced. The 

 velocity of the blast issuing from a tube *8 cm. in diameter 

 was 800 cm. per second, and the wire was charged to a 

 potential of 35 volts. With this velocity the rate of leak of 

 the wire was only one third of the natural leak ; so that two 

 thirds of the conducting particles of one sign were blown out. 

 The length of the exposed wire B D (fig. 1) was 6*3 cm., and 

 knowing the diameter of the wire B D and of the cylinder, it 

 can be shown that the velocity of the conducting particles for 

 air is about 1 cm. per second for a potential gradient of one 

 volt. This is of the same order as the rough determination 

 made in the previous paper by Professor Thomson and myself. 



The positive and negative conducting particles of air travel 

 with the same velocity, for when the sign of the charged 

 wire is reversed the rate of leak is the same as before with 

 the same velocity of the blast. When different amounts of 

 positive and negative electrification were obtained, it was at 

 first thought that part of the difference might be due to 

 inequality in the velocity of the ions, but later experiments 

 showed that it was entirely due to the greater facility with 

 which metals discharged the negative electrification. 



Volume -Density of Electrification of the Charged Gas, 



Only a very minute portion of the gas conveys the charge 

 in the cases we have been considering. In the paper pre- 

 viously referred to it has been shown that assuming the 

 conducting particles convey an atomic charge, only about 

 one billionth of the gas is required to be split up to give the 

 conductivity observed. In the previous experiments the 

 conducting air is still further diluted by the blast along the 

 electrode which conveys the charged particles with it. From 

 data of the capacity of the electrometer and velocity of the 

 blast it can be shown that the amount of charge per c.c. 



