64 



PEOCEEDINGS OF THE AMERICAN ACADEMY 



nickel, when chemically pure, is practically straight, at least between 

 -j- 60° C and — 60° C. 



A thermoelectric element of pure copper and nickel can therefore 

 be used as an accurate means of measuring low temperatures. 



Examination of Ether Thermometer. 



After the preceding experiments the ether thermometer was more 

 critically examined. The bulb was placed in a mixture of calcic 

 chloride and snow, beside the bulb of a mercury thermometer ; and 

 afterwards in water, which was heated to about ■+ 30° C. 



The results are contained in the following table. The first column 

 gives the temperatures shown by the mercury thermometer ; the 

 second column the corresponding temperatures shown by the ether 

 thermometer. 



The zero point of the ether thermometer was determined by bury- 

 ing the bulb in melting snow for twenty minutes. It was then found 

 that the true zero was 2° above the zero of the scale. Applying this 

 correction to the preceding results, it is still seen that the ether ex- 

 panded and contracted very irregularly. 



It is true that only the bulb of the thermometer was subjected to 

 the different temperatures; but the bulb was very large in proportion 

 to the base of the tube, and as an ether thermometer must necessarily 

 be made rather long, it is, in the great majority of cases, impossible to 

 subject any more than the bulb to the temperature to be determined. 



