of Electricity through Gases exposed to Rontgen Rays. 397 



about 10 -1 electrostatic units, or 1/3 X 10 11 electromagnetic 

 units, and this quantity is sufficient to electrolyse all the 

 electrolytic gas produced by the Rontgen rays. Now 1 elec- 

 tromagnetic unit of electricity sets free 10 ~ 4 grammes of 

 hydrogen, or about 1 c. c. at atmospheric temperature and 

 pressure. Hence 1/3 x 10 n electromagnetic units correspond 

 to about the same number of cub. centim. of hydrogen ; the 

 volume of the space between the electrodes was about 10 c.c, so 

 in this experiment the fraction of the gas electrolysed was only 

 1/3 x 10 12 , i.e., one three billionth of the whole amount of the 

 gas. It is not surprising that some experiments we made to 

 see if any alteration in pressure was produced when a gas 

 was transmitting Rontgen rays should have given negative 

 results. The preceding estimate gives the average number of 

 conducting particles ; if the conducting state is intermittent 

 there may at certain times be a much larger number of these 

 molecules present. It is probable that at all events, when the 

 current is saturated the conducting power is intermittent. 

 The action of the coil used to send the discharge through the 

 vacuum tube is intermittent ; thus, if between the passage of 

 two sparks the conductivity has time to vanish (and when any 

 current is passing through the gas the rate at which it 

 vanishes is very rapid) the gas will be alternately an insulator 

 and then a conductor. 



The following experiment is explained by the intermittent 

 character of the discharge. The gas exposed to the Rontgen 

 rays was in a piece of lead tubing open at both ends ; this 

 was connected with one terminal of a battery, the other 

 terminal of which was connected with a ware running down 

 the axis of the tube. A blast of air was blown through this 

 tube, and it was found that when the current between the 

 wire and the tube was small, the blast diminished the current 

 to a large extent, though a current approaching saturation 

 was hardly affected by the blast. When the current was 

 affected the gas blown out of the tube was conducting; when 

 the current was not affected the gas did not conduct. If the 

 gas were exposed to steady radiation it would not be affected 

 by blowing unless the time taken by the gas to acquire the 

 conducting state under the influence of the rays was com- 

 parable with the time taken by the gas to pass through the 

 tube ; this is inconsistent with what we know from other 

 experiments as to the rapidity of action of the rays. If, how- 

 ever, the state of the gas is intermittent, then, since the blast 

 continues w 7 hen the rays are not acting, it blows out conduct- 

 ing gas, and so diminishes its average conductivity. 



To return to equation (3), if I is the value of i when E 



