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PROCEEDINGS OF THE AMERICAN ACADEMY. 



which they have established between the position of the maximum in the 

 energy curve of the spectrum of a source of light and its temperature. 

 Assuming the radiating substance in the flame to have the properties of 

 a black body, they find this temperature in the case of the candle flame to 

 be 1687°, a value seventeen degrees above that which I have given. 



To account for the fusion of Wollaston wire in the flame of a candle, 

 one might consider the possibility of the existence in such a flame of 

 layers of gas the temperature of which is much above the surrounding 

 regions, and that these layers may be so thin that it would not be possi- 

 ble to submerge the thermo-junction completely in them. In such a case 

 the junction would give a value approximate to the average of the tem- 

 peratures of the gases with which it was brought into contact. Before 

 assuming this structure of the flame, which really has nothing to support 

 it save the necessity of accounting for the apparent discrepancy which I 

 have just pointed out, it seemed wise to consider, on the other hand, 

 whether the melting-point of the Wollaston wire was necessarily that of 

 pure platinum. Such wires would naturally be made of ordinary com- 

 mercial metal, the melting-point of which might vary considerably from 

 that of the purer platinum used in the determination of melting-points. 

 It is likewise readily conceivable that in the process of drawing within 

 the silver coating, a certain amount of silver might be worked into the 

 pores of the platinum and not be removed by the subsequent action of 

 the nitric acid. The determination of the melting-point of even such 



minute wires is fortunately a simple matter 

 by means of the form of thermo-element 

 used in the calibration experiments already 

 described. It is only necessary to wrap a 

 piece of the wire to be tested around the 

 junction, as shown in Figure 15, to cut it off 

 so that the end of the loop extends slightly 

 (about 0.05 cm.) beyond the face of the 

 junction ; and having mounted the juuction 

 in the usual manner, to move the acetylene 

 up to it by means of a micrometer screw. I 

 performed this experiment with a piece of the same Wollaston wire 

 which I had succeeded in melting in the candle flame, and found its 

 melting-point, as indicated by the electro-motive force of the junction, to 

 be 1674°. To test the question whether this very low melting-point 

 was due to the presence of silver undissolved by the nitric acid, a piece 

 of the same wire was left in the acid for twelve hours, after which the 



Figure 15. 



