144 



LAWRENCE R. PROUTY AND JAMES D. HARDY 



With the cold junction at 0°C. and the hot junction at t°C. the two 

 constants, B and C, may be calculated by determining the thermo- 

 electric force for two different temperatures of the warm junction. 

 The corresponding temperature may then be calculated for any other 

 observed thermoelectric force. 



Neutral temperature 



Fig. 2. Relationship of thermoelectric force to tem- 

 perature difference between hot aud cold junctions. 



2. Measurement of Thermoeiectric Force 



Either of two fundamental methods may be employed in a variety 

 of ways to measure the thermoelectric force. These are: (a) the 

 galvanometric method, and (b) the potentiometric method. 



Galvanometric Method. This is the simpler and less accurate 

 of the two methods, the thermocouple leads being connected to 

 terminals of a galvanometer. Sensitive pointer galvanometers are 

 now available, although for the mo«t sensitive work lamp and scale 

 galvanometers are required. In some instances, electronic or opti- 

 cal amplification can be employed and temperature changes as small 

 as 0.000001°C. can be detected. The absolute limit of sensitivity 

 is determined by Brownian motion of the galvanometer coils or the 

 Johnson noise of the resistors in the electronic circuit. For quantita- 

 tive measurements it is often convenient to arrange the amplification 

 so that a change of 1°C. corresponds to an even number of scale di- 

 visions. For example, the amplifying system can be adjusted so 



