JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. V APRIL 4, 1915 No. 7 



PHYSICS. — Characteristics of radiation pyrometers.^ George K. 

 Burgess and Paul D. Foote, Bureau of Standards. 



Although this investigation, which is largely made up of 

 instrumental details, does not readily lend itself to a brief sum- 

 mary, yet the following conclusions of a general nature may be 

 mentioned. 



The Stefan-Boltzmann law E = {T^ — T\) is not, in general, 

 except by accident, obeyed in its exactness by any of the pyrom- 

 eters examined. The similar equation E = a. T\ V'-\ in which 

 h is slightly different from 4 (usually neglecting the T^ term) 

 is, however, obeyed with sufficient exactness by all total radia- 

 tion pyrometers. 



The main factors influencing the value of the exponent h 

 are the geometry and mechanical construction of the instrument ; 

 the value of h for* 20 thermoelectric pyrometers ranged from 

 about 3.5 to 4.5. The same instrument of the Fery type may 

 have a different exponent according to its use with or without 

 the sectorated diaphragm for increasing the temperature range. 

 In general, a radiation pyrometer behaves not as a "black" or 

 total receiver of energy, but as a ''gray" receiver for the ordi- 

 nary range of temperatures. For the Fery pyrometer with a 

 gold mirror, for example, the effect of selective reflection of the 

 gold mirror does not become practically appreciable until above 

 2500°C. but may cause an error of 500°C. at the temperature of 



1 To appear as a Scientific Paper of the Bureau of Standards. 



233 



