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Physics. ''(hl lilt' tiiciisiuwnicn.t of riTi/ ioir /t'l/i/x'ni/iiri's. XVMI. 



I )i'tiTninialioiix for /I'sii/u/ 'purposes irilli lite lii/diUKirn tlicrnni- 

 iiKiliT (111(1 the resisf.tincc tlicrnioinetcr. Coiimiuiiioalioii N". lOl" 

 from tlic Pliysicjil hxl)oratoiy al Loidcn l)_v Prof. II. Kamkklinou 

 Onnks, C Ukaak and .]. Clay. 



(Cominiuiicaied in the meermg of November 30, 1907). 



§ 1. Introduction. 



In commnnication N". 95*^ (Nov. i90B) tlie resnlts of a number 

 of nieasnremeiits are recorded which sliow the i)0ssibility of measuring 

 temperatures down to — 217° with the hy(h-o^en tliermometer accu- 

 rately to — de»'. The resuUs ohiained widi sevei-al (illinfts showed 

 50 ^ 



tliat with our measurements to — 217° tliis accui-acy has been I'cached 

 indeed. It was our phxn to make also the following measurements: 



i^K more testing determinations between and — 217° in order 

 to establish still better the limit of the accuracy of the temi)erature 

 measurements with the hydrogen thermometer and the accuracy of 

 the definition ^) once for all of SjX'cial temperatui-es b} definite 

 resistances of a i-esistance thermometer; 



2""^^. the extension of the testing determinations to measurements 

 in lif|uid hydrogen; 



o"\ the determination of definite standard temperatures by means 

 of the boiling points and melting points of hydrogen, oxygen and 

 other substances that can be easily purified. ") 



4ti> (comp. Comm. W. 95" § 1, Sept. 1906) temperature measure- 

 ments with the helium thermometer, a. foi' a direct or an indirect 

 comparison with the hydrogen thermometer, /;. in order to get a firm 

 basis for the determination of the lowest temperatures, especially 

 with a view to the reduction to the absolute scale. 



The investigation mentioned sub 3 and 4 has advanced a good 



1) In investigations tlie reading of temperatures with a resistance thermometer 

 will as a rule for simplicity be preferred to reading them with the hydrogen 

 thermometer. 



-) When we possess the fixed points meant here, the hydrogen thermometer 

 can for calibrations be replaced by boiling point apparatus filled with pure gas and 

 ])laced in tlie same bath as the apparatus to be calibrated. This is a great sim- 

 plification in cases where only these fnv special tempeiatures are required. 

 Moreover in these fixed points we have the means for a comparison between gas 

 thermometers filled with different gases (for instance Ho and He) or between 

 thermometers in different laboratories. 



