542 Adams and Johnston — Standard Scale of Temperatures. 



sively, that there is no systematic deviation whatever, within 

 the range of these measurements, between the readings of 

 these two kinds of thermometers — either at boiling points or 

 at melting or freezing points — when both are calibrated with 

 reference to the same temperature scale. 



This position is confirmed by a direct comparison of the 

 series of measurements by Waidner and Burgess of the resist- 

 ances of platinum thermometers with the recent gas thermome- 

 ter measurements of Day and Sosman,* transferred by means 

 of thermoelements to the same fixed points. So far we have 

 dealt with temperatures less than about 330° ; but the compari- 

 son just referred to enables us to extend the same conclusion 

 to the copper point (1083°), beyond which the readings of the 

 resistance thermometer are no longer trustworthy. 



Comparison of the Series of Resistance Thermometer Measure- 

 ments ( Waidner and Burgess) with Gas Therinometer JDeter- 

 rninations {Day and Sosman) at the same Fixed JPoints. 



For a fair comparison it is essential that the results be 

 expressed in the same scale of temperatures ; for this we have 

 adopted the thermodynamic scale. We have accordingly 

 applied the appropriate corrections, taking a mean of the cor- 

 rection numbers collated by Buckingham, f 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. 



The results as given by Waidner and Burgess^ were derived 

 by means of the Callendar formula,§ the third calibration tem- 

 perature being the sulphur 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 simulta- 



* This Journal, xxix, 93-161, 1910; Carnegie Institution of Washington, 

 Publication No. 157, 1911. Cf. also preceding paper. 



[Bull. Bur. Standards, iii, 288-9, 1907 ; (reprint No. 57). 



Xlbid., vi, 150-223, 1910, (reprint No. 124); vii, 1-11, 1910, (reprint No. 

 143). 



§The Callendar formula is t— pt — 6 ( — — l)y™, where t is the true 



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

 relation 



100 (R t - Bo) 

 Pt =—E p~ 



(R is the resistance at t°). 6 is a deviation constant derived by means of the 

 formula from the third calibration temperature (usually the sulphur boiling 

 point) ; for pure platinum 6, as thus obtained, is close to T50. The formula 

 is essentially a simple quadratic relation of the form 

 R t — R + at + bt> 



