319 



« 



has been shown", however, that the rehition between temperature and cur- 

 rent through the lamp may be represented by the general quadratic equa- 

 tion 



I = a -|- bt + ct^ 

 so that three known temperatures are sufficient to completely calibrate the 

 instrument. Such a pyrometer may be readily calibrated, without the use 

 of a black body, by means of a standard pyrometer comparison lamp as 

 explained above. If such a lamp is not properly calibrated in terms of 

 temperature and current its black body temperature, for any value of 

 current, may be determined by means of another calibrated pyrometer. A 

 platinum ribbon may be used in the same way. 

 Physics Laboratory , 

 Ftirdue Uni versi ty. 



11 Bulletin, Bureau of Standards, Vol. I, p. 2o!j. 



