98 PROCEEDINGS OF THE AMERICAN ACADEMY. 



best an indefinite character from which studies of acetylene are free. In 

 the latter case we have to deal with a definite fuel, and the velocity of 

 the jets of gas from the burner is sufficient to give a high degree of sta- 

 bility to the flame. 



The caudle would seem an even less satisfactory subject of study in 

 these respects than illuminating gas, but the fact of the melting down 

 of Wollaston wire, the verification of which I have briefly described in 

 an earlier paragraph of this paper, seemed to discredit so completely the 

 low values commonly given that I decided to redetermine its tempera- 

 ture by the method already described. 



The fact that the flame of a candle, mounted upon a fixed stand, 

 would move steadily downward as the material of which it was com- 

 posed burned away, made it convenient, without any serious modifications 

 of my apparatus, to explore the temperature of the luminous sheath 

 throughout the entire length of the flame. It was only necessary for 

 this purpose to mount a candle upon the steel bar in the position previ- 

 ously occupied by the acetylene flame, and when it had reached such a 

 length that the level of the rim of the cup lay below the level of the 

 junction, to move the candle toward the latter by means of the microm- 

 eter screw until the junction began to be submerged in the luminous 

 sheath of the flame. It was then easy by a series of slight adjustments 

 of the flame to explore with the junction the eutire surface of the lumi- 

 nous sheath from base to tip, measuriug temperatures from time to 

 time, and determining the position by means of the height of the junc- 

 tion above the rim of the candle cup. The latter observations were 

 readily made by means of the image of the candle upon the ground 

 glass of the camera. Explorations of the candle flame in the manner 

 described were made with Junctions II. and IV., and the results obtained 

 showed a degree of consistency much greater than the fluctuating char- 

 acter of the source under observation had led me to expect. Both sets 

 of observations showed a maximum of temperature in the same region : 

 that lying just above the tip of the interior dark zone of the flame. 

 Readings were made by watching the movements of the candle flame 

 and securing a balance of the potentiometer at times when the face of 

 the junction was as nearly as possible in contact with, but not deeply 

 submerged within, the luminous layer. Whenever the wire plunged to 

 any considerable depth beyond the luminous surface, deposition of soot 

 occurred with lowering temperature, and it was necessary to withdraw 

 the junction into the non-luminous regions outside and to wait until the 

 deposit had been burned off, before proceeding with the readings. In 



