1178 



it gives a curve vvhicli lias its concave side towards the <9-axis. It 

 cannot serve, therefore, as a foriiiuia of reduction for Pt — 21 and 

 Pt—I^ (comp. table V, colunm B on the previous page). 



A,v mav be represented tVoni ()° to — 240° C. by the formula 



n 



10' . Liy :r: — 1-400 . 6» — 0-35 . 1 Qioo .... (8) 

 (conip. table V, column A on the pievions page)') 



II. H. Kamkklingh Onnes and G. Hoi.st found some time ago 

 that the curve which represents the deviations from the linear formula 



6 = — 243 + 243 — == - 243 (l — w) .... (9) 



' 



shows a pretty considei-able bend in the region of the lowest tempe- 

 ratures which may be reached with liquid oxygen"). This bend is 

 closely connected with the point of inflexion discussed in Comm. N". 95. 

 As the jneasurements could not be extended beyond — 21H° (!. 

 at that time, it was impossible to study the deviation at lower 

 temperatures. We are now in a position to supplement this investi- 

 gation by giving in fig. 3 the curve showing the deviations from 

 (he linear formula for the two platinum thermometers Pt — 21 and 

 Ft — 26'). It appears that below —220° C. the deviation becomes 

 very considerable and the steepness of the curve shows clearly 

 that the abo\ e linear relation cannot be used in this region for the 

 calculation of temperatures. 



III. Comparison of the wires in the temperature-region of liquid 

 hydrogen. 



The wires Pt—B (comp. Comm. NMI9 p. 19), Ptv and P^— 21 

 were compared with Pt — 26 in the range from 14.2 to 20.5 K. 

 For this purpose the following quadratic interpolation-formula was 

 established for Pt — 26 : 



^) Table V contains besides the values of AIV as given by the measurements 

 (comp. table 111) the values calculated from the exponential formula (8) (column A) 

 and those calculated from Clay's formula (7) with C= — 0.00305^. This value 

 of G is computed from the value of A/r at e - — 188°. 95 (in accordance vs^ilh 

 Jahrb. Rad. u. Elektr Xll p. 261. 1915). 



The differences between Aoès and ^ccdc iB) rise to 0.00021, corresponding to 

 a temperature difference of about 0.05 of a degree. 



In fig- 2 the functions corresponding to the formulae (8) and (7) are represented 

 by the curves IV A and IV B respectively. 



2) Leiden Gomm. N**. 141a, p. 9. These Proc. XVII (1) p. 506. 



5) The curve represents 



A = — 243 (1 —lo) — 6 

 as a function of 0- 



81* 



