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THE ROYAL SOCIETY OF CANADA 



in turn at the temperatures given respectively- by (a) water (b) naphtha- 

 lene, (c) mercury and (d) sulphur boiling at atmospheric pressure, 

 and finally (e) at the temperature of melting zinc. 



Figure 1 



These temperatures and the corresponding electromotive forces 

 obtained with the couple are given in Table I. A calibration curve 

 drawn from them is shewn in Fig. 2. 



TABLE I. 

 Calibration Readings. 



This curve it will be seen is linear only over the lower ranges of 

 temperature and indicates that a maximum electromotive force would 

 in all probability be obtained with the thermocouple at or slightly 

 above 500° C. The values usually given in the tables for the electro- 

 motive forces given by a nickel iron thermo-j unction shew that the 

 relation between temperature and electromotive force for this couple 

 should be a linear one. Such results, however, were obtained no 

 doubt, with nickel and iron which had been specially purified. 

 In the present investigation, the nickel and iron wires used were those 



