Titanium, and Vanadium by Thermelectronic Currents. 257 



and bands which compose it, unlike those emitted by tKe 

 luminous vapours previously described, pass only a short 

 distance down from the graphite plate and stop quite 

 abruptly, as though the exciting agent had suddenly ceased 

 to act. Evidently then, this spectrum cannot be entirely 

 controlled by the plate temperature, as otherwise its lines 

 and bands, like those of the luminous vapour emission, 

 would die out only gradually. We must therefore trace 

 its origin to some other cause, and it is only natural to 

 connect the emission of this spectrum with the formation of 

 the red fringe. A direct experimental proof for the reality 

 of this connexion will be given in § 9. Thus, the emission of 

 the carbon bands and of the lines of titanium and vanadium 

 is in some way caused by the thermelectronic current which, 

 at these high temperatures, passes through the strongly 

 ionized vapours in the immediate vicinity of the graphite 

 plate. The emission would therefore be due to what I have 

 previously called thermo- electrical excitation *, and it is no 

 doubt of the same nature as that which I had preconceived 

 to exist in a high temperature tube resistance-furnace. 



The spectrum of the red fringe and of the luminous 

 vapours are reproduced on Plate II. The narrow strip of 

 sharply defined and strong continuous ground, which forms 

 the upper edge of each section, is due to the luminous 

 emission by the exposed edge of the incandescent graphite 

 plate. The ultra-violet end a was obtained with the special 

 furnace arrangement in which the vapours beneath the plate 

 are better protected from air currents, and sections b and c 

 with the clamping bars described in § 2. In this latter case 

 the vapours are more exposed to air draughts and therefore 

 the spectrum lines # do not pass down quite so far. In the 

 zone of the red fringe the two emissions are naturally seen 

 in superposition, but by reason of the abrupt extinction of 

 the lines and bands which compose the red fringe spectrum, 

 the separate existence of each emission is clearly brought out. 

 Some of the low temperature lines are seen in absorption upon 

 the continuous spectrum due to the edge of the graphite 

 plate. This is of course caused by the constant stream of 

 excess vapour which is being carried upwards in front of the 

 plate by the aforesaid air currents. It is also well to draw 

 attention to the behaviour of the H and K lines of calcium. 

 These lines are seen to pass down a much shorter distance 

 from the plate than neighbouring iron lines of equal or 

 even less intensity, such as the group at 3920. They are 



* Hemsalech, Phil. Mag. xxxvi. p. 295 (1918). 

 Phil. Mag. S. 6. Vol. 39. No. 231. March 1920. S 



