82 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



high temperatures, it is necessary to make a thorough calibration of the 

 individual thermo-elements involved, or at least of the set of elements 

 manufactured from any given sample of metal. How important it is to 

 perform such a calibration for one's self may be seen from the fact that 

 Ilolman, Lawrence, and Barr* obtained an electromotive force of .0303 

 volts from a platinum, platinum-rhodium (10%) element at the tempera- 

 ture of melting platinum, whereas a similar element constructed of wire 

 from Heraeus gave in the hands of the present writer .0182 volts at the 

 same temperature. 



Numerous more or less complicated methods of calibration involving 

 the use of various forms of the gas thermometer have been proposed, 

 the carrying out of which involves the use of special apparatus which 

 is difficult of construction and laborious in operation. Fortunately it was 

 possible in the present investigation to substitute for these a new and 

 easy method in which the acetylene flame itself was the source of heat. 

 This method t possesses the advantage of extreme simplicity, and it 

 affords indications the accuracy of which leaves little to be desired. 



The acetylene flame em pi »yed was of the usual flat form produced by the 

 union of two impinging jets. There are three distinct stages observable 

 in the form of such a flame, depending upon the pressure at which the gas 

 is supplied to the burner. In the first, we have two separate cylindrical 

 jets of small size (Figure 4 a), which, with increasing gas pressure meet 

 without uniting, each being deflected, by impinging upon the other, into 

 a vertical plane (Figure 4 b). At still higher pressures the actual union 

 of the two jets takes place, giving the flame the structure shown in (Fig- 



* Holman, Lawrence, and Barr, J. Am Acad, of Arts and Sciences (1895), 

 p. 218. 



t This method of calibration has been separately described in a contribution to 

 the Lorentz Jubilee Volume. The Ha cue, 1900. 



