236 TABLE 242. 



CORRECTION FOR TEMPERATURE OF MERCURY IN THERMOMETER 



STEM. 



The Stem Correction is proportional to /3( T /) : where n is the number of degrees in the 

 exposed stem ; /3 is the apparent coefficient of expansion of mercury in the glass ; T is the measured 

 temperature ; and t is the mean temperature of the exposed stem determined by another ther- 

 mometer, exposed some 10 cm. from, and at about half the height of, the exposed stem of the first. 



For temperatures up to iooC, the value of ft is for : 



Jena glass XVI ra or Greiner and Friedrich resistance glass, ^ or 0.000159; 



Jena glass 59, or 0.000164. 



6300 



At 100 the correction is in round numbers 0.01 for each degree of the exposed stem ; at 200 

 0.02 ; and for higher temperatures proportionately greater. At 500 it may amount to 0.07 for 

 each exposed degree. 



Tables 242-244 are taken from Rimbach, Zeitschrift fiir Instrumentenkunde, 10, 153, 1890, and 

 apply to thermometers of Jena or of resistance glass. 



TABLE 242. -Stem Correction for Thermometer of Jena Glass (0-360 0.). 



Degree length 0.9 to i.i mm; /=the observed temperature; /'=that of the surrounding air 

 i dm. away ; n = the length of the exposed thread. 



SMITHSONIAN TABLES. 



