510 



Dr. R. S. Willows on the 



Fio-. 6. 



on the inside by precipitating silver from silver nitrate and its 

 rate of running down again determined. In order to prevent 

 the discharge from passing along the silver, either directly or 

 by means of platinum sputtered from the wires passing through 

 the glass, these wires were enclosed in the soft glass used to 

 fasten them into the tube. The rate at which the pressure 

 decreased was the same as before the silver was deposited on 

 the surface. 



It was found that air, nitrogen, and hydrogen all gave the 

 same rate of running down. 



Another tube was lined with mica, but this produced no 

 difference in the rate of absorption. 



7. The effect of keeping the discharge from striking 

 directly on the glass composing the tube 

 was investigated by means of the tube 

 shown in fig. 6. 



It consisted of a tube about 3*5 cm. 

 diameter, having an aluminium-wire elec- 

 trode A sealed into the closed end. 

 This electrode was entirely surrounded by 

 the other electrode B, which consisted of 

 a cylinder of thin sheet aluminium, the 

 upper end of this cylinder being closed 

 by another flat, circular piece. 



In order to make the discharge take 

 place well inside the cylinder, the bottom 

 of the electrode A was fused into a thin 

 covering of soft glass. When this was 

 done the discharge passed directly from 

 metal to metal. The tube had to be run 

 hard for several weeks before regular 

 readings could be obtained. When this 

 stage was at last reached, the following 

 results were obtained. 



It was found that when A was the anode there was hardly 

 any absorption of air, but when A was cathode the pressure 

 decreased as before. At pressures near 1 mm. the absorption 

 was appreciably quicker with this tube than with those pre- 

 viously used ; probably, had the regularity of the readings 

 permitted a close comparison, it would have been found that 

 this held throughout the whole range. 



When B was cathode the whole tube was hot during the 

 passage of the current, considerably more so than when the 

 current passed in the opposite direction. 



To show that the fall in pressure is not altogether due to 

 oxidation of the metal, the experiment was repeated with 



^o 



