80,000 



28.000 

 26,000 

 24,000 

 22,000 

 20,000 



14,000 



the Roberts- Austen Recording Pyrometer. 71 



Holborn and Wien, and Holman, Lawrence, and Barr have 

 also been plotted. An examination of figure 5 shows that 

 very serious discrepancies exist between the indications of 

 couples having- the same nominal composition. Thus the 

 thermo-electric power of the 10 per cent, rhodium thermo- 

 couple of Holborn and Wien was only about 3/5 of that 

 obtained by Holman, Lawrence, and Barr ; and the 10 per 



Fisr. 5. 



ELECTROMOTIVE FORCE OF THERMOCOUPLE! 

 OF PLATINUM AND PLATINUM ALLOYED 

 \0% OF RHOD'UM OR IRIDIUM 



cent, iridium couple employed by the author had about 2^ 

 times the thermo-electric power of a 10 per cent, iridium alloy 

 examined by Barus. Through the kindness of Colonel 

 Edward Matthey, the author has been able to investigate the 

 causes of these discrepancies, which are too large to be 

 attributed merely to the accidental differences in the per- 

 centage of rhodium or iridium in the platinum alloy used. 



Two 10 per cent, rhodium alloys were prepared and drawn 

 into wires from which the thermo-couples, Nos. 15 and 16, 

 were made up with a return wire of pure platinum common to 



Je<i*"' "(WO* 



