Titanium; and Vanadium by Thermelectronic Currents. 253 



§ 5. Influence of a transverse magnetic field upon the 

 visibility of the red fringe. 



If, as has been assumed, the red fringe were caused by the 

 passage of an electric current outside the plate, it should be 

 acted upon by a transverse magnetic field. In order to test 

 this graphite plates were mounted between the hollow field 

 coils of an electromagnet in such a way, that the heating- 

 current flowed at rio'ht angles to the direction of the lines of 

 magnetic force. The temperature of the plate was raised to 

 about 2700° C, at which stage the red fringe is ordinarily 

 not yet visible. As soon, however, as a magnetic field of 

 from 125 to 175 C.G.s. units was put on with the force acting 

 upon the heating current in a downward sense, the red fringe 

 immediately appeared. On taking the magnetic field off, the 

 red fringe disappeared. On reversing the direction of the 

 magnetic field, no red fringe was observed. One would 

 have expected, in this latter case^, to see a red fringe appear 

 above the plate, but undoubtedly, owing to the prevailing- 

 convection currents, the vapours do not become sufficiently 

 ionized under these temperature conditions to allow of the 

 passage of an electric current. But when the plate was 

 raised to a temperature of about 3000° C, so that the. red 

 fringe was well visible beneath the plate even without the 

 aid of a magnetic field, then the application of an upward 

 acting magnetic force of 1300 C.G.s. units brought out a red 

 fringe above the plate, whereas the fringe beneath the plate 

 practically disappeared. On taking the field off again the 

 red fringe above disappeared, whereas at the same time that 

 beneath the plate reappeared. By applying Fleming's hand- 

 rule it was easy to show that the displacements of the red 

 fringe were quire in accordance with the laws of electro- 

 magnetic induction, which is a direct proof that the red 

 fringe is governed by the flow of an electric current. 

 Furthermore, the appearance of the red fringe cannot be 

 governed by temperature alone, for otherwise it would mean 

 that when a magnetic field of from 125 to 175 units acts in 

 the downward sense upon the plate at 2700° C. its tempera- 

 ture should increase by about 300° C, which, as the results 

 of my temperature determination (§ 3) clearly show, is not 

 the case. 



But, in addition to these facts and arguments in favour of 

 the electrical nature of the red fringe, a most important 

 factor, which also gives strong support to this view, is the 

 following observation made when the red fringe was acted 

 upon by a transverse magnetic field in a downward sense : — 

 luminous streamers were seen to pass out of the fringe into 



