2S2 Mr. G. A. Hemsalech : Excitation of Spectra of Carbon, 



5. Spectroscopic examination has revealed the existence of 



two entirely different and distinct emissions by the 

 luminous vapours in the neighbourhood of the heated 

 plate. One of these emissions is controlled by the 

 plate temperature and is due to thermo-chemical 

 excitation. The lines and bands which compose its 

 spectrum are observed to die out only gradually on 

 passing away from the plate. The second emission is 

 confined to the immediate vicinity of the plate, and 

 in extent it coincides with the red fringe. It is 

 further shown that this emission is controlled by the 

 thermelectronic current and is therefore due to thermo- 

 electrical excitation; The characteristic feature of its 

 spectrum is that its lines and bands, unlike those of 

 the first emission, stop quite abruptly at the lower 

 edge of the red fringe. § 7 and § 9. 



6. The spectrum of the first emission (thermo-chemical 



excitation) is composed of the lines or bands of the 

 more volatile metals, such as Na, Li, Sr, K, Al, Oa, 

 Mn, Fe, etc. ; that of the second emission (thermo- 

 electrical excitation) is constituted of the bands of 

 carbon, the lines of titanium and vanadium, and a 

 group of characteristic red bands of very hazy 

 appearance. § 7. 



7. The gradual development of the carbon spectrum with 



thermo-electrical excitation is in the reverse order to 

 that observed with chemical excitation. It is further 

 pointed out that this spectrum is not emitted by the 

 hottest parts of the mantles of the air-coal gas, oxy- 

 coal gas, and oxy-acetylene flames. Consequently, it 

 is not excited by thermal or thermo-chemical actions 

 up to a temperature of 2700° 0. § 7. 



8. The sharp outline presented by the red fringe is caused 



by the magnetic field around the plate due to the 

 heating current. This magnetic field has a tendency 

 to drive the thermelectronic current back towards the 

 plate, and it thus prevents the diffusing downwards of 

 even the least part of this current. § 8 and § 9. 



9. A discussion of the thermal, electric, and magnetic con- 



ditions existing in the vicinity of an electrically heated 

 plate, as compared with those prevailing in the interior 

 of a tube resistance furnace, has led to the inevitable 

 conclusion that thermelectronic currents will be enabled 

 to pass through the ionized vapours in the latter already 

 at a comparatively low temperature, and moreover, 

 they will diffuse without difficulty throughout the 



