Titanium, and Vanadium by Thermelectronic Currents. 267 



due to the heating current. Only traces of the carbon bands 

 and titanium lines are now visible in the vicinity of the plate. 



The next two photographs, on Plate IV., were obtained 

 with a plate temperature of about 3000° C, at which the red 

 fringe is ordinarily well developed. a was taken with a 

 magnetic field of 590 C.G.S. units acting upwards. The rela- 

 tive intensification and the sharply marked boundary line of 

 the fringe spectrum make it appear as though the stream of 

 emission centres created by the thermelectronic current were 

 being pressed up against the graphite plate by the acting 

 magnetic force. This is, of course, quite in agreement with 

 tbe views expressed in the preceding paragraph. It is well 

 also to draw attention to the fact that the lines of the second 

 emission — namely, that given out by the luminous vapour 

 and caused by thermo-chemical excitation — continue to die 

 out gradually on passing away from the plate, in spite 

 of the magnetic field. b shows the fringe spectrum 

 under the same conditions as regards temperature and 

 strength of magnetic field, except that the magnetic force 

 is pulling the thermelectronic current downwards. With 

 this strong field the thermelectronic current spreads to a 

 very considerable distance from the plate and it is in- 

 teresting to note that under these conditions the lines and 

 bands of the fringe emission do not stop abruptly but die 

 out only slowly (comp. §8). The continuous spectrum and 

 the lengthening of the vapour lines are again due to the 

 spiral paths of luminous particles carrying electric charges. 



In all the experiments described so far in this paragraph 

 the luminous effects due to the thermelectronic current were 

 observed only beneath the graphite plate and, even with a 

 magnetic field of 590 C.G.s. units acting upwards, no trace of 

 the fringe spectrum was ever seen above the plate. Stronger 

 magnetic fields exerted such a pull on the thin graphite plates 

 that the latter invariably broke before the necessary tempera- 

 ture was reached. But by using shorter plates, having an 

 effective length of only 21 mm., fields of up to 1300 C.G.s. 

 units could be applied for a sufficient length of time to secure 

 a photographic record. In this way it has been possible to 

 observe the red fringe above the plate and to obtain the 

 photograph of its spectrum which is reproduced on Plate V. 

 This record, I believe, constitutes the most striking and con- 

 vincing proof for the electrical origin of the fringe spectrum. 

 I was unable to ascertain whether the emission of the fringe 

 spectrum above the plate is due to a thermelectronic current 

 having passed out from the upper surface (covered with a 

 layer of carborundum) or, what is perhaps more likely, to 

 the forcing upward, round the side of the plate, of part of 



