NICHOLS. — THE VISIBLE RADIATION FROM CARBON. 95 



1800 



1600 



1400 



1200 



100 200 300 



CROSS-SECTION OF WIRES 



Figure 12. 



400 



ordinates. If these curves could be extended to the Hue representing zero 

 cross-section, the temperatures indicated by the points in which each of 

 them cuts that line would give the temperature of the portion of the 

 flame to which the curve corresponds. There is a considerable element 

 of uncertainty in extrapolation even over so short a range as this : but it 

 is obvious from the character of the curves lying within the limits of 

 observation, that each of them trends upward, and it seems highly prob- 

 able that they all meet the line of zero cross-section at a temperature not 

 far from 1900°. The fact that the curves cut this line at nearly the 

 same temperature would seem to indicate that the distribution of tempera- 

 tures from the centre of the flame outward for a distance of about 1 mm. 

 is a nearly uniform one. 



It would perhaps be unwise to attempt to draw any more definite con- 

 clusion from the probable trend of these curves; but I have ventured to 

 extend them in the manner shown in the figure, so that the curve for the 

 region 1 mm. from the centre of the flame reaches the zero of abscissae 

 about, twenty degrees above that for the centre of the flame, i. e. at 1920°, 

 and. the intermediate curves at temperatures lying between them. I 

 regard this as an extreme treatment of the case, and allude to it only to 

 indicate that, in accordance with common belief, the highest temperature 



