Physics. — "On fh,' jncasinunm'nl of wri/ Imr ft'inpcrffhires.X'KlV'. 

 The hydrogen and heUuni thermometers of constant volume, 

 down to the freezing-point of hydrogen compared with each 

 other, and with the platinum-resistance thermometer. By Prof. 

 H. Kamerlingh Onnes cand G. Holst. Communication NM41rz 

 from the Physical Laboratory at I;eiden. 



(Gommimicated in the meeting of May 30, 1914). 



§ 1. Introduction. The measurements which this paper deals 

 with bring the investigations undertaken in Leiden for Ihe purpose 

 of eslablisliino- the scale of the absolute temperatures as far down 

 as the freezing point of hydrogen, to a conclusion, in so far that a 

 direct comparison lias now been made between the helium and 

 iiy drogen scales, by measurements with a differential thermometer, 

 which had the object to test the corrections to the absolute scale of 

 temperatures below 0° C, obtained separately for the helium scale 

 (in XIX of tills series) and the hydrogen scale (partially given in 

 XVIII of tiiis series')). For the place which the mutual control of 

 these corrections occupies in the more general investigation of the 

 measurement of low temperatures which is being carried out in 

 Leiden, we refer to § 6 Sup[»l. N". 34a. The test could be extended 

 as far as the freezing point of hydrogen, after the compressibility 

 of hydrogen vapour had been determined by Kamerlixgh Onnrs and 

 DR Haas, Coram. N". 127c. (June 1912) -). Our comparison of the 

 helium scale with the hydrogen scale') by means of the differential 

 thermometer to which was added a new calibration of the Leiden 

 standard platinum thermometer Pti (formerly Pti) shows that a 

 very satisfactory agreement has been attained in the temperature 

 determinations. 



') Compare also H. Kamehlingh Oxnes, G. Braak and J. Clay, Comm. 

 N". 101a. (Nov. 1907) § 1 under \b. 



~) In this Comm. a difference was discussed which existed between the tempe- 

 rature determination with a hydrogen thermometer according to the resistance 

 thermometer Ptt, which was calibrated by means of it and the temperature deter- 

 mination by extrapolation of the isotherms. According to calculations by Dr. 

 Keesom, suggested by Sackur's interesting investigation, this deviation might be 

 connected with the theory of quanta (Comp. Suppl. N". 30 and N". 34a § 11). 



•^) The comparison of the hydrogen and helium thermometers by Travers, 

 Senter and Jaquerüd, Phil. Trans. A 200 (1903), p. 105, has been discussed 

 in Comm. N°. 102. hi general their results are in good agreement with our 

 measurements. 



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