216 Prof. H. L. Callendar on Platinum Thermometry. 



We select for this purpose the following data : — 

 Thermometer in Melting Ice, 

 E/R°= 1-000, *=0°C. 

 Thermometer in solid C0 2 at 760 mm., 



R/R° = -800, ^=-78-2° C. 

 Thermometer in Liquid 2 at 760 mm., 

 R/R° = -523, *=-182°-5 C. 

 From these we deduce the folio wing values of the coefficients : — 



a=-002515, b = --000,000,53, c = '002462, rf=2-13, 

 pi°=406°-2. 



As a verification we have the observation R/R° = *453, at 



£=-208°'5 C. This gives pt= -222% D=13°'7 ; which 

 agrees with the value given by the difference-formula calcu- 

 lated from the three higher points. 



The following Table owes the reduction of the observations 

 taken with this thermometer in partially liquid hydrogen. 



Table III. — Reduction of Olszewski's Observations 

 in Boiling Hydrogen. 



Pressure. 



R/E°Obs. 



pt. 



D. 



t (° C). 



t Olszewski. 



t'. 

 -233°4 



atmos. 

 20 



•383 



-250°6 



16°6 



-23°4-0 



-234-5 



10 



•369 



-256-3 



17-3 



-239-0 



-239-7 



-238-4 



1 



•359 



-260-4 



17-7 



-242-7 



-243-5 



-242-0 



The effect of this change in the method of reduction is to 

 make the temperature of the boiling-point of hydrogen nearly 

 one degree higher than the value given by Olszewski. If we 

 employ instead the difference-formula in terms of pt, we should 

 find c' = -002472, pt° = 404°'5, d'=l'85. This formula leads 

 to the values given in the column headed t' , which are a little 

 higher. 



The value found by Dewar for liquid hydrogen (Proc. R. S. 

 Dec. 16,1898) is much higher, namely t= — 238° # 8 at one 

 atmo, and — 239°*6* at l/30th atmo. The difference may 

 possibly be due to the superheating of the liquid, or, more 

 probably, to some singularity in the behaviour of his thermo- 

 meter at this point (see below, p. 218) . 



Observations of Holborn and Wien (Wied. Ann. lix. 1896). 

 — Holborn and Wien made a direct comparison between the 



* Values calculated from observed resistances by formula (2). 

 gave 



Dewar 



