Cady — On the Energy of the Cathode Hays. 3 



Faraday cylinder C, which was connected to earth. The rays 

 entered through the hole <?, 6 mm in diameter. R is the glass 

 discharge-tube, 25 cm long, cemented to the glass plate P. 



The copper bottom of the brass tube K served as cathode ; 

 in order to reduce the heating as far as possible, a stream of 

 water was kept constantly flowing through the tube. The 

 anode A was a zinc diaphragm. 



r 7 



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M 



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The discharge current was furnished by a secondary battery 

 B of 2288 cells, supplemented at times by a'rotary transformer, 

 so that a maximum E. M. F. of 5400 volts could be reached. 

 The current was regulated by the Hittorf cadmium-iodide 

 resistance 7, and the potential of the cathode measured by 

 means of the quadrant-electrometer E. G is a Thomson gal- 

 vanometer used in measuring the thermal and cathode-currents. 



A serious source of error in observations lay in the evolution 

 of gas from the cathode and other parts of the apparatus dur- 

 ing discharge. This difficulty, so common in all gas-discharge 

 work, was nearly always present, even after the apparatus had 

 been in use for many hours. A partial remedy was found 

 in running the air-pump slowly during observations, but 

 even then the potential usually changed somewhat during the 



