879 



Professor H. Kamkrmngh Onnes. The lemperatnres were measured 

 wiUi the aid of a platimim j'esistaiice-thermomefer. The wire was 

 about 0,1 mm. in diameter and was wonnd bifilarly on a small tube 

 of Marquardt-material on which a double spiral groove had been 

 t:ut. At the ends of the tube stouter platinum wires were auto- 

 genioally sealed on; to these wires the four copper leads were 

 soldered. Before using the thermometer it had been treated thermally 

 by a tenfold immersion in liquid air, each time followed by glowing 

 at about 700°. By that means a constant zero-point was obtained. 

 On three different days the resistance lo^ was found equal to 

 J 8.4695 «, J 8.4697 « and J 8.4695 .Q respectively ; it was measured 

 with a differential galvanometer by Kohlrausch's method. 



The calibration of the thermometer took place by using the vapour- 

 pressures of oxygen as determined by Kamert.ingh Onnes and Braak, ') 

 in the apparatus in which the end-points of the condensation were 

 determined. If /> represents the vapour-pressure in mms., the relation 

 between T and p in the range 83,5° and 90° abs. is:'') 



369,83 



T = . 



6,98460 — loff. p 



w 

 The ratio — was determined at the same time. 



For the Leiden standard platinum thermometer ft\ the ratio — 



as a function of the temperature in the range of tempei-atures in 

 question is accurately known. It is therefore possible to calculate 

 the value of the constant a in the linear relation which according 

 to Nernst holds for different thermometers: 



1 — 



With <f=r 0,00121 our thermometer could be reduced to Pt\a.\\é 

 this constant was therefore used in calculating the temperatures. 



To test the apparatus which served for the determination of the 



points of beginning condensation for its utility, the boiling point of 



oxygen was also determined in it. The pressure was 762.4 mm. 



According to the vapour-pressure formula this corresponds to a 



?(' 

 temperature of 90°.15 ; the ratio gave 90°. 16, which agrees very 



"•o 



closely. As « was conqiaratively small for our thermometer ^) and, 



1) H. Kamerlingh Onnes en Braak. Gomm. Leiden No. 107a. 

 -) G. Holst. Coram. Leiden No. 148a. 



8) H. ScHiMANK, (Ann. d. Phys. (45) 706, 1914), gives 0.1-0.2= as the 

 uncertainty for x = 0.03. 



