184 Mr Whiddington, Some fatigue effects 



The first experiments accordingly were made with cocoanut 

 charcoal electrodes. 



Two circular carbon electrodes of equal thickness and about 

 two centimetres in diameter were mounted symmetrically and 

 parallel in a vertical straight tube only slightly larger, so as to 

 face each other at a distance of about 30 centimetres. A sub- 

 sidiary aluminium electrode was fused in, in a side tube midway 

 between the two cathodes. Further, each carbon electrode was 

 arranged so as to be at the geometrical centre of a concave alu- 

 minium electrode, which, when run as cathode, bombarded its 

 attendant carbon electrode with an intensely heating beam of 

 cathode rays. 



The upper electrode was taken as the standard. The lower 

 electrode was heated up by the convergent beam of rays from its 

 concave cathode, the resulting spot of incandescence being moved 

 about by means of a bar magnet. After four or five hours' 

 continuous heating and pumping the carbon ceased to give off 

 gas, indicated by the width of the Crookes' dark space remaining 

 constant. 



The spectroscope showed the emitted gas to be mainly oxides 

 of carbon with a perceptible trace of hydrogen. 



The tube now contained an upper electrode full of gas, and a 

 lower one free of gas. The two electrodes were then connected 

 direct to the secondary of an induction coil (giving a 6 in. spark). 

 On making alternately the upper and lower carbon electrodes, 

 cathode, no difference in the character of the discharge could be 

 detected. The cathode ray emission as roughly indicated by the 

 green glass phosphorescence was the same and the Crookes' dark 

 space was in both cases of* the same width. 



Now, on running the lower carbon as cathode for 10 minutes, 

 the subsidiary side electrode being anode, a further small quantity 

 of gas was given off indicated by the shrinking in of the dark 

 space. As before the gas appeared to be oxides of carbon and 

 hydrogen. 



A comparison of this now further depleted lower carbon with 

 the standard showed a distinct alteration in properties. The 

 green glass phosphorescence was very much less brilliant and the 

 Crookes' dark space narrower and more sharply defined. After 

 20 minutes running as cathode, this fatigue effect, as it may be 

 called, became more marked ; but after half an hour the cathode 

 seemed to get into a constant state. The state of affairs can be 

 summed up in few words by saying that the upper standard 

 cathode behaved as though the tube were hard, the lower one as 

 though the tube were soft, yet the gas pressure was the same in 

 either case. 



The fact that the boundary of the Crookes' dark space 



