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Physics. — „On the measurement of very low temperatures IV. 
Comparison of the platinum thermometer with the hydrogen 
thermometer,” by B. MetLiNk. (Communication n° 77 from 
the Physical Laboratory at Leiden by Prof. H. KAMER- 
LINGH ONNES). 
§ 1. The research on the relation between the electric resistance 
of platinum and, the temperature (below zero) considered in this 
paper forms a part of a more general investigation including some 
other metals, which will be treated in following papers. It seemed 
advisable to divide this entire investigation into two parts, viz. 
Ist to express as accurately as possible the resistance as a function 
of the temperature for a standard metal, for which purpose platinum 
offers great advantages ; 
2nd to express as accurately as possible the variation due to 
temperature, in the ratio between the resistances of several perfectly 
pure metals or metals with certain known small impurities and the 
resistance of the standard metal (platinum). 
The absolute determinations mentioned under 1 consist of a com- 
parison of the platinum thermometer with the hydrogen thermometer, 
a subject with which OLszewsk1'), HOLBORN and Wr…eN ®), Dewar 
and FLEMING and lately HoLBorn *) again have been occupied. 
S 2. Arrangement of the resistance thermometer. 
The hydrogen thermometer with which my resistances have been 
compared, is described in Communication n° 27, viz. the one with 
the reservoir of 90 ce. In the main the observations are made as 
related in n°. 60. From the agreement of the pressure coefficient 
of hydrogen, deduced from the investigations described there, with 
that of CHAPPUIS, it appears that a high degree of accuracy can 
be attained in this way. Under favourable circumstances the tem- 
perature can be determined to within 0.02 deg. C.; even for the 
boiling-point of oxygen the uncertainty remains less than 0.03 deg. C. 
In terms of resistance this corresponds to about 1/39 °/o at —180° C. 
and 1/199 % at O° C. Therefore the determinations of resistance were 
arranged so that this accuracy could also be attained with the 
absolute determinations. 
Even if we increase without special arrangements the accuracy 
of the determinations of resistance, and perhaps also that of the 
1) Akademie der Wissenschaften in Krakau. Juni 1895. 
2) Wied Ann. 59. S. 222. 1896. 
9) Ann, der Physik 6. S, 252. 1901, 
