60 



Mr. A. Stansfield on some Improvements in 



following paper, and the experiments were conducted in the 

 laboratory of the Royal Mint. 



Introduction. 



An excellent summary of the early work on pyrometry is 

 given by Barus in his elaborate paper " On the Thermo- 

 Electric Measurement of High Temperatures " *, published in 

 1889, so that it will only be necessary here to consider briefly 

 the present condition of high-temperature measurement. 



Arrangement of the Apparatus. 



The ultimate standard of temperature is afforded by the 

 air-thermometer ; nearly all other instruments are referred to 

 this either directly or indirectly. Apart from the air-thermo- 

 meter, which is not well adapted for ordinary use, there are 

 two systems of pyrometry suitable for exact measurements of 

 temperature. One of these, which depends on the change 

 * Barns, Bull. U.S. Geol. Survey, no. 54. Washington, 1889. 



