Prof. J. J. Thomson on Cathode Hays. 



295 



enough negative electricity went through the narrow slit into 

 the inner cylinder in one second to alter the potential of a 

 capacity of 1*5 microfarads by 20 \olts. If the rays were so 





Fis:. 1. 



awj 



B 



Earth 



Electrometer 



much bent by the magnet that they overshot the slits in the 

 cylinder, the charge passing into the cylinder fell again to a 

 very small fraction of its value when the aim was true. Thus 

 this experiment shows that however we twist and deflect the 

 cathode rays by magnetic forces, the negative electrification 

 follows the same path as the rays, and that this negative elec- 

 trification is indissolubly connected with the cathode rays. 



When the rays are turned by the magnet so as to pass 

 through the slit into the inner cylinder, the deflexion of the 

 electrometer connected with this cylinder increases up to a 

 certain value, and then remains stationary although the rays 

 continue to pour into the cylinder. This is due to the fact 

 that the gas in the bulb becomes a conductor of electricity 

 when the cathode rays pass through it, and thus, though the 

 inner cylinder is perfectly insulated when the rays are not 

 passing, yet as soon as the rays pass through the bulb the air 

 between the inner cylinder and the outer one becomes a 

 conductor, and the electricity escapes from the inner cylinder 

 to the earth. Thus the charge within the inner cylinder does 

 not go on continually increasing ; the cylinder settles down 

 into a state of equilibrium in which the rate at which it gains 

 negative electricity from the rays is equal to the rate at which 

 it loses it by conduction through the air. If the inner 

 cylinder has initially a positive charge it rapidly loses that 



