1012] on Very High Tcmpvraiures. 327 



The electrodes were insulated as before, and into the annular space 

 between them hydrogen or nitrogen was continually passed. No 

 potential was applied, and the currents we obtained with a steadily 

 rising temperature and a new carbon electrode are shown in Fig. G. 

 It will be seen that there was first a small " positive " current (which 

 would be ])roduced by positive ions crossing from the hot to the cold 

 electrode), which soon changed into a much larger " negative " current 

 (in the usual direction) ; the intensity of the latter dropped, and 

 then showed a progressive increase with temperature. On taking 

 down the apparatus we found that the brass tube was coated over 

 most of its length with a thick and coherent deposit of carbon which 

 had evidently crossed over from the hot electrode. Towards one end 

 the deposit was rarer and whitish — presumably silica. We associate 

 the maximum negative current of Fig. 6 with the passage of silicon 

 and other impurities, which are volatilized at about 2000° C. out of 

 the carbon electrode. On a second heating neither positive rays nor 

 a negative maximum were detected, but the ionization current increased 

 steadily with temperature. The transference of carbon from the hot 

 electrode to the cold may prove to be a complete explanation, not 

 only of the contamination phenomena which gave rise to these experi- 

 ments, but also of the comparatively large accompanying currents. 



Fig. 7 illustrates the results obtained when steps had been taken 

 to increase the difference of temperature between the hot and cold 

 electrodes. The carbon was new, and the negative maximum again 

 appears. Afterwards the furnace temperature was steadied, and the 

 ionization current also kept steady in consequence. It will be noticed 

 that we were now dealing with currents amounting to large fractions 

 of an ampere, and the experiments may fairly be regarded as pro- 

 viding a novel means of generating electricity. Their direct bear- 

 ing on the problems of the electric arc and the carbon filament lamp 

 is obvious, and we are continuing the research with a view to eluci- 

 dating the many underlying phenomena. 



[J. A. H.] 



