Titanium, and Vanadium hy lliermelectronic Currents. 283 



whole inner space of the tube, because the magnetic 

 field due to the heating current is zero. Furthermore, 

 the character and order of development of the carbon 

 spectrum in the tube-furnace, as compared with that 

 in the red fringe, indicate plainly that, also in the 

 furnace, its emission is caused by thermelectronic 

 currents. § 11. 

 10. It is pointed out that the disagreement between the 

 furnace results obtained by Dr. King and myself is 

 most probably due to the different arrangements em- 

 ployed. Dr. King's furnace tube, being unprotected, 

 requires a greater heating current and consequently 

 a stronger electric field to raise it to a given tempera- 

 ture than is necessary for a furnace tube which is well 

 protected against heat losses by means of a carborundum 

 jacket. Further, by using alternating current for heating 

 the tube, the electric field reaches a maximum value 

 of 1*4 times that given at the same temperature with 

 continuous current heating. For these two reasons 

 the maximum acting- electric field in Dr. King's 

 furnace is twice as strong as in mine for any given 

 temperature. Hence, lines or bands the origin of 

 which can be directly traced to the action of therm- 

 electronic currents, such as the carbon bands and 

 class III. lines of iron, will in the unprotected alter- 

 nating current furnace show already at much lower 

 temperatures than in a well-protected continuous 

 current furnace. § 12. 



§ 14. Concluding Remarks. 



The present investigation has furnished most conclusive 

 results in evidence of the emission, by the tube resistance 

 furnace, of luminous radiations which depend for their exci- 

 tation upon electric actions. It has further been shown that 

 the spectroscopic effects produced in this way are governed 

 by the acting electric field and the state of ionization of the 

 vapours. They depend upon the furnace temperature only r 

 in so far as the latter controls the electrical conductivity of 

 the vapours. If the furnace be well protected from loss of 

 heat and be worked with continuous current, the electric 

 field which is established at the lower temperatures may be 

 too small to stimulate those atomic vibrations which are 

 sensitive to electric actions. This has been shown to be the 

 case with iron. If, on the other hand, the tube of the fur- 

 nace be left unprotected and be heated with alternating 



