280 ADAMS AND JOHNSTON: STANDARD TEMPERATURE SCALE 



a mean of the correction numbers collated by Buckingham, 8 to 

 the results of Day and Sosman, which were determined on the 

 constant volume scale. The uncertainty of the gas thermometer 

 determinations is indeed comparable with the magnitude of these 

 corrections; nevertheless we have, for the sake of definiteness, 

 considered it advisable to apply them. 



TABLE III 



Comparison of Temperature Intervals as Measured by Thermoelements 

 and by the resistance thermometer 



* When reading only to 1 microvolt, as we were, it is illusory to give the readings 

 of the platin-rhodium element closer than the nearest tenth of a degree. 



The results as given by Waidner and Burgess 9 were derived by means 

 of the Callendar formula, 10 the third calibration temperature being the 

 sulfur boiling point taken as 444?70. In order to refer these values to 

 the comparison scale, it seemed simplest to substitute in the Callendar 

 equation the simultaneous values of the thermodynamic temperature 

 (t) and the platinum temperatures of a single resistance thermometer 11 



8 Bull. Bur. Standards, 3: 288-9. 1907; (reprint No. 57). 



9 Ibid, 6 : 150-223. 1910; (reprint No. 124) ; 7 : 1-11. 1910; (reprint No. 143). 



. / t \ t 



10 The Callendar formula is t — p — o I 1 ) —— , where is the true tempera- 

 ture, and pt (the so-called platinum temperature) is defined by the relation 



_ 100 (Rt-Ro) 

 Rioo — Ro 

 (Rt is the resistance at t°). 5 is a deviation constant derived by means of the for- 

 mula from the third calibration temperature (usually the sulfur boiling point) ; 

 for pure platinum 5, as thus obtained, is close to 1.50. The formula is essentially a 

 simple quadratic relation of the form 



R t = Ro + at-bt 2 . 



11 No. 1787C; this instrument was used over the widest range and appears to be 

 the most satisfactory of those used at the Bureau of Standards. 



