( 299 ) 



in the <\ase of iiilrno-en boiling- iiiidoi- i-educed pressure, however, 

 tlie deviulioii lias Wccoiik' \en' large, so large cncii lliat it raiinol 1)0 

 explained l»v ei'i'ors of observation. Hence the cii'cunislance that the 

 tbnnnla is not tit to represent the resistance so near to the absohite 

 zero must accouid t'oi- this deviation. All the same it is remarkable 

 that this turn app(;ars so suddeidv. At 197 ('. the torninla still 

 holds, at 2H) ('. there is a deviation of 2"29 on l(;()2r), i.e. a 

 deviation of 0".49 in tenijKM-atnre. lint if we take into consideration 

 that, according- to I he fornnda, the i-esistance at 243° 0. wonld 

 become zero and that we are onlv aboul tliirlv degrees from this 

 point, we need not wonder at this result. 



In order to gain certainty tJiat there was indeed a fairly ra{)idly 

 increasing variation in the shajie of the curve that repi-esents the 

 resistance as a finiction of the lenipei-aliire, I resoKcd to repeat 

 especially these measnremejits at vevy low lempeialiire in nitrogen. 

 These constitute what I haxe called at the begimiing the 2°^ series. 

 Unfortunately the result was unsatisfactory. 



Though the observations indeed point in the same sense, yet one 

 error or another seems to have crept into them and it c(ndd no 

 more be detected at the time when the calcnlations revealed it. We 

 shall omit them here. 



Therefore the results as to the amount of the deviations remain 

 more or less nncei-tain ; yet it is very probable that even in nitrogen 

 boiling under reduced pressure, a beginning may be obser\ed of the 

 variation in the course of the temperature function which, as follows 

 from Dewar's experiments, appears so strongly at the temperature 

 of liquid hydrogen. 



The conclusions to which the measurements lead may be summarized 

 as follows. 



A representation of the resistance by a (jiiadratic forunila, according 

 to the temperature, even if we do not go below — '180°C., is only 

 permitted when no higher degree of accuracy than (V.2 C'. is aimed 

 at. When a greater precision is desired we re( pure for the calibration 

 of a platimun thei-monieter a greater number of points of comparison. 



1 



For a comparison to within ^ ^ t^- ^^ number of at least 6 tempera- 



tures of comparison is considered very desirable. 



Below — 197'' (^ the deviations of the platiiuim thermometer 

 become so large that before using it for this range an investigation 

 must be made of the course of the resistance as a function of the 

 temperature. 



