408 



Mr Rutherford, The Discharge of 



[Feb. 21, 



Experiments performed in this way give a value of the 

 velocity of the carrier at normal pressure of about 



1'5 cm. per sec. 



for a potential gradient of 1 volt per cm. This method is 

 however probably not capable of accuracy, on account of the 

 variation of the velocity of the air across the cross section of the 

 plates and accidental disturbances due to the violent eddying 

 motion of the air when velocities of the order of 300 or 400 cm. 

 per sec. are used. The method is also practically restricted to 

 the case of air on account of the large amount of gas required 

 for an experiment, so that I was led to devise a more general 

 and satisfactory method of determining the velocity of the carrier. 

 In Fig. 3 the general arrangement is shown : a glass bell-jar 



was fixed on a base plate CD of zinc through which a circular 

 opening EF was cut. In the top of the vessel there was fixed 

 an ebonite stopper through which passed a rod L carrying at one 

 end a polished metal plate AB. This plate A B was fixed to a 

 ball-and-socket joint, and could be levelled by screws passing 



