TABLES 192-193. 

 CORRECTION FOR TEMPERATURE OF EMERGENT MERCURIAL 



THERMOMETER THREAD- 



When the temperature of a portion of a thermometer stem with its mercury thread differs 

 much from that of the bulb, a correction is necessary to the observed temperature unless the 

 instrument has been calibrated for the experimental conditions. This stem correction is pro- 

 portional to nft(T - /), where n is the number of degrees in the exposed stem, ft the apparent 

 coefficient of expansion of mercury in the glass, T the measured temperature, and / the mean 

 temperature of the exposed stem. For temperatures up to 100 C, the value of is for Jena 

 i6i" or Greiner and Friedrich resistance glass, 0.000159, for Jena 59"', 0.000164, and when of 

 unknown composition it is best to use a value of about 0.000155. The formula requires a knowl- 

 edge of the temperature of the emergent stem. This may be approximated in one of three ways: 



(1) by a "fadenthermometer" (see Buckingham, Bulletin Bureau of Standards, 8, p. 239, 1912); 



(2) by exploring the temperature distribution of the stem and calculating its mean tempera- 

 ture; and (3) by suspending along the side of, or attaching to the stem, a single thermometer. 

 Table 192 is taken from the Smithsonian Meteorological Tables, Tables 193-195 from Rimbach, 

 Z. f. Instrumentenkunde, 10, p. 153, 1890, and apply to thermometers of Jena or resistance 

 glass. 



TABLE 192. Stem Correction for Centigrade Thermometers. 

 Values of o.oooissn(T f). 



TABLE 193. Stem Correction for Thermometer of Jena Glass (0 to 360 C). 



Degree length 0.9 to i.i mm; / = the observed temperature; t' = that of the surrounding air 

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



SMITHSONIAN TABLES 



