AND LIQUIDS AND THEIR VARIATION WITH TEMPERATURE. 



411 



For convenience of interpolation the numbers headed " ohms per degree " are taken 

 as ordinates, and 6 + #o as abscissae, of the curves which follow the table. 



CONSTANTS of Thermo-j unctions. 



*/ 



40 

 S3 



Ohms -se 



P er -S7 



degree. , M 



30 40 



so eo ro so 



90 IOO IIO ISO OO I4O ISO 160 



It will be noticed from the table that although the wires used for the thermo- 

 junctions were cut from the same bobbins and treated alike subsequently, the 

 thermo-circuits had different constants, the difference in the case of the upper and 

 middle circuits amounting to 1 per cent., and in the case of the upper and heater 

 circuits to 6 per cent. 



This prevents the difference of the temperatures of two junctions being determined 

 directly by dividing the electromotive force in circuit when the junctions are placed 

 in series, by a constant. The method to be used is indicated subsequently. 



The "cover" and "upper" circuits were found to give identical results, and the 

 upper junction was therefore adopted as the standard, and the differences between its 

 electromotive force and those of the other junctions determined in each case. 



To determine the temperature of the junction in the upper disc, given the 

 temperature of the junction in the mercury cups, and the electromotive force in the 

 circuit, we require to divide this electromotive force by a quantity which itself 

 varies to a small extent with the temperature required. If, however, this tempe~ 



3 G 2 



