Adams and Johnston — Standard Scale of Temperatures. 543 



neous values of the thermodynamic temperature (t) and the 

 platinum temperatures of a single resistance thermometer* as 

 measured by Waidner and Burgess, and to compute in this 

 way the corresponding values of $'. These values vary irreg- 

 ularly at the lower temperatures, as might be expected, since 

 the influence of variation of 8 is small when t is small ; but at 

 the higher temperatures they show a distinct upward trend, and 

 can be represented very fairly by the relation 8' = 1-489 + 

 0*000015 t. These values of 8' were combined with the respec- 

 tive platinum temperatures to give new values of the temper- 

 ature, which were then subtracted from the temperatures as 

 given by Waidner and Burgess ;f thus giving the differences 

 between the two scales at these points. These differences 

 were applied to the average values given by Waidner and 

 Burgess, giving the " corrected" average temperatures pre- 

 sented in Table Y, column II. Alongside of this we have 

 tabulated (column I) the temperatures on the thermodynamic 

 scale as derived from the work of Day and Sosman, and (in 

 column III) the differences between these two sets of measure- 

 ments. 



The differences at the tin and zinc points are no doubt due 

 to the fact that in these two cases the determinations were 

 made on different samples of metal ; with these two slight 

 exceptions the agreement is all that could be desired. This 

 concordance shows further that if we derive an interpolation 

 formula for the resistance thermometer based on all of the 

 points excepting sulphur, and calculate by means of this formula 

 the boiling temperature of sulphur, we obtain a result identical 

 with the direct gas thermometer determination of this fixed 

 point. 



If we recalculate the above temperatures, using a fixed value 

 of 8 based on the newer determinations of the sulphur point, we 

 obtain results which are practically identical with those of 

 column II (Table Y) except at the silver and copper points, 

 which would on this 'basis be. lower by 0*6° and 0'9° respec- 

 tively. This silver point would still be within the limits of 

 accuracy of the gas thermometer measurements at that point, 

 but the divergence at the copper point (1'3°) is somewhat 

 greater than the probable error. 



This raises the question of the range through which the 

 simple, and very convenient, Callendar formula is applicable 

 in accurate work. It does not hold for impure platinum or 

 for palladium ;J nor does it hold for pure platinum at all tem- 



*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. 



f That is, the temperatures as derived from a fixed 6, obtained by calibra- 

 tion at 0°, 100°, and the S b.p. taken as 444'70°. 



% Waidner and Burgess, Bull. Bureau Standards, vi, 176, 183. 



