Titanium, and Vanadium by Thermelectronic Currents. 255 



field set up by the heating current, as explained in § 8. The 

 origin of the red fringe emission would thus be, in some way, 

 connected with the process of generation of these atom-ions. 

 As it will be necessary, especially for spectroscopic purposes, 

 to make a clear distinction between the thermionic current 

 and that producing the red fringe, I propose to call the 

 latter the thermelectronic current. 



§ 7. Spectroscopic analysis of red fringe and luminous 



vapours. 



A two-fold magnified image o£ the incandescent graphite 

 plate and the luminous phenomena below it was accurately 

 i'ocussed on the slit of the spectrograph, already described in 

 a previous communication *. The image was adjusted in 

 such a way that the slit passed through the middle part of 

 the plate and perpendicularly to it, as indicated by the 

 dotted line on fig. 4. By this means the spectral changes 

 occurring along the distance from the hottest part in the 

 immediate vicinity of the plate, down to the region of com- 

 plete extinction of the luminous vibrations, could be observed 

 at a glance or recorded photographically. The times of 

 exposure for the photographic records varied from 3 seconds 

 at the highest to over half a minute at lower temperatures. 



The spectrum of the vapours which form beneath the plate 

 is of course due to the elements contained in the graphite 

 and carborundum as impurities, probably in combination 

 with carbon as carbides. At lower temperatures appear 

 the lines of Na, K, Li, Sr, Ca, Mn, Al, and Fe, and the 

 whole spectrum is observed to grow progressively .in in- 

 tensity and development as the plate temperature gradually 

 rises. In addition to the line spectrum there is also seen 

 a continuous spectrum which is particularly strong near 

 the lower edge of the bluish vapour and extends to the 

 same distance downward as the latter. Now, the lines 

 emitted by the various impurities expelled from the graphite 

 and carborundum generally pass well below the border of 

 the continuous spectrum ; this indicates that their emission 

 centres travel to a greater distance from the plate than the 

 bulk of the bluish vapour. Hence there appears to be no 

 direct connexion between the line emission observed and the 

 sharply bordered cloud of bluish vapour described in § 4. 

 It is possible that the bluish vapour is formed only along the 

 boundary surface of the protected space, constituting as it 

 were a kind of envelope, and that the emission centres, to 



* Heinsalech, Phil. Mag. vol. xxxiii. p. 7 (1917). 



