NICHOLS. THE VISIBLE RADIATION FROM CARBON. 99 



computing the actual temperatures of the luminous sheath of the flame 

 from these readings, I contented myself with the following rough ap- 

 proximation. The maximum temperatures shown by Junctions II. and 

 IV. were plotted upon the same diagram used for the luminous »as 

 flame. These temperatures were 1281° and 154G ; values which, as 

 will be seen by inspection of -Figure 14 (c), lie much below those of the 

 corresponding readings for the luminous gas flame, but in such position? 

 as to make it easily possible to draw through them a curve analogous 

 in form to that obtained for the latter. Such a curve would cut the 

 line of zero cross-section at about 1670°, which may, I believe, be taken 

 as the approximate temperature of the hottest portions of the luminous 

 sheath of the candle flame. Estimates of this temperature by the prob- 

 ably less accurate methods of drawing a straight line through the points 

 in question and taking the point in which this line cut the line of zero 

 cross-section to be the temperature of the flame, and estimates based 

 upon the assumption that the true temperature is as many degrees above 

 the temperature indicated by Junction IV. for the candle as it is for the 

 gas flame, would lead to values respectively twenty-four degrees and 

 forty degrees lower than that obtained by the method which I have 

 adopted. I believe that the temperature just given (1670°) is much 

 closer to the truth than that obtained under either of the other assump- 

 tions. Estimated temperatures for other portions of the luminous sheath 

 were made by assuming that the correction to be applied to the readings 

 obtained with Junction IV. would be the same in all positions. TIi 

 values are given in Figure 14 which may serve in place of an ordinary 

 table. The portions of the flame to which each reading refers are 

 more readily indicated by giving such a diagram of the flame than in 

 any other way. 



The fact that, in the case of the acetylene flame and the ordinary gas 

 flame, this method gives values high enough to account, for the melting 

 of platinum, but leads to an estimate of the temperature of the candle 

 flame which is about one hundred degrees below the melting-point of that 

 metal, would seem, at first sight, to throw the procedure into serious 

 doubt. My experience with the method has, however, been such as to 

 make an error of one hundred degrees in the estimation of the candle- 

 flame'temperature seem highly improbable. Messrs. Lurnmer and Pring- 

 sheim, in a recent communication to the German Physical Society,* give 

 an estimate of the temperature of candle flames based upon a relation 



* Lummer and Pringsheim, Verhandlungen der deutschen pliysikalischen 

 Gesellschaft, 1899, p. 214. 



