186 Mr Whiddington, Some fatigue effects 



a little magnet so that the screen could be rotated by an external 

 magnetic control. The screen was midway between the two 

 electrodes. When both electrodes were fresh the phosphorescence 

 of the screen was independent of the cathode from which it 

 received the exciting cathode rays. When, however, one of the 

 electrodes was run as cathode for some time, the Willemite glowed 

 much more vividly when it was responding to rays from the 

 fresh cathode, the dark space being a centimetre or so in width 

 and the distance of the screen about 5 cms. 



This fact lends support to the view that at any rate some of 

 the rays emitted from a fresh cathode are faster and therefore 

 more penetrating than those emitted from a run cathode. 



The surface of the aluminium used in the above (and future) 

 experiments was always polished with the finest emery powder so 

 as to be sure of always having a constant surface. 



It was thought that the observed effects might be merely due 

 to surface influences. This was proved to be not so, by filing off 

 about "2 mms. of the metallic surface and repolishing. The run 

 cathode so treated appeared to be still as fatigued as ever. 



A fatigued cathode also shows no very marked signs of recovery 

 if left to itself In one particular case a tube was left at atmo- 

 spheric pressure for over three months and at the end of that time 

 the fatigue effect was still as obvious as it had been immediately 

 after the running period. 



At first, running the fatigued cathode as anode did not appear 

 to have any effect, but using a very small induction coil (giving 

 5 mm. spark) to produce the discharge, an effect was observed 

 when the pressure was between certain limits. When the fatigued 

 cathode which had been run as anode was made cathode again, 

 there was a sudden burst, so to speak, of phosphorescence when 

 the discharge first passed. This sudden brilliance however was 

 only momentary, lasting but a small fraction of a second. This 

 transient recovery did not seem to depend on the length of time 

 the electrode was run as anode ; making it anode momentarily 

 produced as much effect as running for quite a long time. The 

 effect was most marked in hydrogen but could be got in other 

 gases as well. 



Chrisler in the paper cited quotes figures showing that the 

 photoelectric current for metals increases enormously if the elec- 

 trode is run momentarily as anode in hydrogen. This falls into 

 line with the cathode effect described above, but his further 

 observation that running as anode in gases other than hydrogen 

 actually diminished the photoelectric effect finds no counterpart 

 in these experiments. 



It was thought that the volume of metal forming the cathode 

 might influence the time taken to produce the fatigue effect. 

 Experiments on this point gave no definite results. 



