248 TABLE 278. 



CORRECTION FOR TEMPERATURE OF MERCURY IN THERMOMETER 



STEM. 



The Stem Correction is proportional to ( T t) : where u is the number of degrees in the 

 exposed stem ; is the apparent coefficient of expansion of mercury in the glass ; 7' 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 /8 is for : 



Jena glass XVI 111 or Greiner and Friedrich resistance glass, ? or 0.000159; 



6300 



Jena glass 59, ^ or 0.000164. 



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 278-280 are taken from Rimbach, Zeitschrift fur Instrumentenkunde, 10, 153, 1890, and 

 apply to thermometers of Jena or of resistance glass. 



TABLE 278. Stem Correction for Thermometer of Jena Glass (0-360G.). 



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. 



See " The correction for Emergent Stem of Mercurial Thermometer." Buckingham, Bui. Bur. of Standards, 

 SMITHSONIAN TABLES. 



