V. TEMPERATURE DETERMINATIONS 



153 



methods should be mentioned such as sewing thermocouples into a 

 cotton material stretched over the surface, and attaching the ther- 

 mocouples to a copper screen wire brought into contact with the sur- 

 face (19). Since the thermocouple will only measure its own temioer- 

 ature, it is apparent that it may not be measuring the true surface 

 temperature when moiuited in any of the ways mentioned above. 

 Stoll and Hardy (18) have made a partial analysis of the thermocouple 

 method of measuring surface temperature and, as is seen in Table I, 

 thermocouple thermometers vary considerably depending upon the 



Fig. 8. Application of thermo- 

 couples to small animal calorimetry. 

 Double-walled gradient calorimeter 

 with thermocouples soldered directly 

 to copper walls. (A) Outer shell, (B) 

 inner shell, (C) wire animal cage, (D) 

 thermocouple lead for ingoing air 

 thermometer, (E) outgoing air thermo- 

 couple, (F) pan filled with oil for ani- 

 mal excreta, (G) shell thermocouple 

 leads, (H) inner top showing window, 

 thermocouple leads, and rim for air- 

 tiglit seal to inner shell, (I) outer top 

 with thermocouple leads. 



Air out 



Air in 



Animal Calorimeter 



circumstances under which they are used. It is safe to say that de- 

 pendable measurements of surface temperature cannot be made with 

 thermocouples under all the conditions of the biophysical laboratory 

 and the hospital. This inherent difficulty applies to the measurement 

 of leaf temperatures, wall temperatures, and interface temperatures 

 generally. However, circumstances may be such that the approxi- 

 mation obtained by the thermocouple may be the only practical one, 

 as, for example, the measurement of the skin temperature of man 

 under the clothing. 



Calorimetry. Thermocouples are indispensable for calorimetry 

 studies because of their high sensitivity and low thermal capacity. 

 Recently described gradient calorimeters (4,^0) depend entirely on the 

 sensitivity and accuracy of thermocouples. In the second calorim- 

 eter, the measurement of heat loss depends upon the determination 

 of the temperature difference between two copper C3'linders, the inner 



