NICHOLS. 



THE VISIBLE RADIATION FROM CARBON. 



Ill 



a more prolonged exposure at high temperatures, and that thus it might 

 be possible to extend the measurements beyond the point reached with 

 the rods of black surface. This was found to be the case. 



As has already been indicated in a previous paragraph, the indications 

 of a thermo-junction at these high temperatures was subject to serious 

 suspicion. I was obliged to content myself, therefore, with estimations of 



Figure 22. 



• '> 



the temperature based upon the difference of potential between the ter- 

 minals of the rod. Fortunately the relation between the electromotive 

 force and the temperature up to 1400° was of such a character that but 

 little error was to be feared in extrapolating. The relation between 

 electromotive force in volts and temperature is shown in Figure 21. 

 From this curve temperatures above HOC were determined. 



