244 Mr. E. Rutherford on the Electrification 



current through the gas. In the above table the saturation- 

 value of the E.M.F. was about 70 volts, and this corresponds 

 to the maximum amount of electrification. 



Since the velocity of the conducting particles increases 

 with the E.M.F. but the current through the gas remaius 

 constant, when the E.M.F. is raised above its saturation- 

 value it is to be expected that a greater proportion of the 

 conducting particles would reach the electrode. This agrees 

 with experiment, for as the E.M.F. is increased above a 

 certain value the amount of electrification obtained steadily 

 diminishes. 



The amount of electrification obtained for a given E.M.F. 

 increases at first with the velocity of the blast, and then tends 

 to a maximum, value, which cannot be increased, however 

 rapid a blast is sent along the wire. 



An experiment proving conclusively that the amount of 

 electrification is intimately connected with the conduction of 

 electricity through the gas is as follows : — The electrode along 

 which the air was blown was carefully insulated and connected 

 to one pair of quadrants of the electrometer. The two pairs 

 of quadrants were charged up to the same potential and then 

 insulated from each other, and the rate of leak of the charged 

 wire determined. The rate of leak steadily diminished with 

 increase of velocity of the blast : when the air issuing from 

 the glass tube had a velocity of about 1000 cm. per second the 

 rate of leak was only one fourth of its value when the air was 

 still, and the amount of electrification in the air passing from 

 the wire, as tested bv the glass wool cvlinder. was nearlv 

 equal to the quantity of electricity corresponding to the 

 difference between the two rates of leak. 



We should not expect them to be exactly equal, since some 

 of the Eontgenized air containing both positively and nega- 

 tively charged particles is also blown out. 



The charged gas obtained in this way is thus due to an 

 excess of the positive or negative conducting particles, what- 

 ever they may be. to which conduction in gas under the 

 Eontgen rays is due. 



In all these experiments precautions were taken aoainst dust. 

 It was found tnat the amount of electrification obtained was 

 independent of the quantity of dust in the air provided the 

 velocity of the issuing blast was kept constant. The air in 

 one case was sent through a long tube filled with glass wool 

 into the gas reservoir, which was then allowed to stand for a 

 couple of days without being disturbed. The air in passing 

 from the reservoir to the generator was again passed through 

 glass wool, but the effect obtained was exactly the same as if 



