High Temperatures by the Method oj Colour Identity 55 



As regards the determination of filament temperature by- 

 previous observers, only three sets of determinations, those 

 of Forsythe*, Von Pirani and Meyer f, and LangmuirJ, are 

 given in comparable form. 



In some other determinations no mention is made of the 

 watts per candle or lumens per watt of the lamps tested. In 

 others " black body" temperatures and not true temperatures 

 are given of the filaments radiating in the open§. 



In Table IV. the results obtained by the authors are com- 

 pared with those of the above-mentioned observers. Both 

 Forsythe and Von Pirani only measured the mean horizontal 

 candle-power of their lamps, and a reduction factor of 0*85 

 for carbon and 0*79 for tungsten has been assumed in both 



M.fi.C.P. 



cases for the ratio mwttb-. It will be seen that the 

 M.Jti.L/.-r . 



Table IV. 



Type of 



Lumens 



True Temperature Filament C C. 



lamp. per watt. 



Forsythe. 



Pirani and 

 Meyer. 



The 



Authors. 



Tungsten 



8-0, 

 81 5 

 8-4 4 

 8-8- 



9-0 

 8-8, 

 9 3. 



1,980 

 1,982 

 2.008 

 2,020 

 2.025 

 2,035 

 2.040 



1,820 

 1.847 

 1,843 



2,069 

 2,072 

 2,084 

 2.100 

 2. J 09 

 2,101 

 2,121 



1 ,935 

 1,966 



1,965 



2,010 

 2,014 

 2,027 

 2,041 

 2,051 

 2,044 

 2,063 



1,818 

 1,846 

 1,845 



" 











Carbon 



3-5 2 

 39, 

 3-9 t 



" 



" 



The lumens per watt are obtained from the values of watts per candle 

 given by the authors, by assuming ratios of 0*79 and 085 respectively for the 



reduction factors Uj H UP ) for tun o sten antl carbon lamps. 



The value of 0-9 is taken for the ratio of the Hefner to the British unit of 

 candle-power. 



* Phys. Rev. vol. xxxiv. May 1912. 



t E. T. Z. 1912, May 2, p. 457, and July 11, p. 725. 



X Proc. of Amer. Inst, of Elect. Engineers, vol. xxxii. p. 1895. 



§ Dr. II. Lux, E. T. Z. May 28, 1914, gives tables connecting tempe- 

 rature and watts per mean spherical candle of tungsten lamps. The 

 values given in the table would appear to approximate to true tempera- 

 tures, but the method described for determining the temperatures is that 

 ordinarily used for obtaining black body temperature. Without further 

 information of the methods used by Dr. Lux for the determination of 

 true temperature, a useful comparison with readings of other observers 

 is difficult to make. 



