252 Mr. G. A. Hemsalecli : Excitation of Spectra of Carbon, 



and extending downwards to a distance of from 1 to 2 mm. 

 (fig. .4). For convenience' sake, this luminous band will 

 henceforth always be referred to simply as the red fringe, 

 although there is a distinct violet shade in its colour. 



Fi-. 4, 



+ 



Red -fringe 



Rising vapours 



Carborundum 

 powder^ 



Graphite 

 plate 



Bluish vapours 



Relative position of 

 spectrograph slit. 



Plate Temperature : 3000° C, 



A preliminary examination of the spectrum of the red 

 fringe, which was found to be entirely different both as to 

 character and composition from that given by the luminous 

 vapours situated beneath the fringe, at once suggested 

 thermo-electrical excitation as the cause of its emission. 

 It was therefore provisionally assumed as a working hypo- 

 thesis that, owing to the very great degree of ionization 

 prevailing at this high temperature, part of the heating 

 current had passed out of the graphite plate into the space 

 below and that its path was revealed by the formation of the 

 red fringe. 



