V. TEMPER A T I' R E DETER M I N A T I O X S 165 



A new type of radiometer for measuring the radiation temperature 

 of the outdoor environment has recently been described by Richards 

 and Hardy (31). This instrument consists of three spheres, black, 

 white, and polished, into which electrical energy is fed to bring them 

 all to the same temperature. This gives a measurement of radiation 

 from which the "wall temperature" of the environment may be com- 

 puted. « 



4. Limitations of Radiometers 



The apijlication of a radiometer is limited almost entirely to the 

 measurement of surface temperatures in biophysics, and for this single 

 purpose it is beyond question the best instrument. Radiometers 

 are fragile instruments and require relatively expensive electrical 

 equipment for measurement of radiation. Emissivity values must 

 be worked out for each type of surface to be investigated and correc- 

 tions often must be applied to the radiometric readings due to re- 

 flected and scattered light. 



F. MISCELL4NEOUS TEMPERATURE MEASURING 



DEVICES 



All the followng temperature measuring devices have some bio- 

 physical application although limited to some particular problem. 

 The discussion is therefore brief. 



1. Thermoluminescence 



Many chemical compounds emit fluorescent radiation within a 

 narrow temperature range only. Zinc sulfide produces yellow fluores- 

 cence between and 123°C. The fluorescence of zinc oxide changes 

 from red to green at 704° C. The quality and quantity of fluores- 

 cence of the microorganisms found in the slime forming on certain 

 decaying fish changes to a marked degree as the environmental tem- 

 perature is altered. Many other substances have other characteristic 

 fluorescent temperatures and, if these critical points hajipen to fall 

 near those of some biophj'sical reaction, they may be useful indicators. 



2. Dielectric Constant Changes 



The dielectric constant of most compounds is a function of tem- 

 perature. A ceramic capacitor such as titanium dioxide, Ti02, for 



