236 Table 242. 



CORRECTION FOR TEMPERATURE OF MERCURY IN THERMOMETER 



STEM. 



The Stem Correction is proportional to nfi[T—l) : where « 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 i 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 ioo°C, the value of ^ is for : 



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



6300 



Jena glass 59™, -, — or 0.000164. 

 ■^ *• ^^ 6100 ^ 



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 Gorrectlon for Theimometer of Jena Glass (0°-360°C). 



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

 I dm. away; « = the length of the exposed thread. 



Smithsonian Tables. 



