( 208 ) 



Snppl. K°. 9, Febr. '04). And this has been done especially becanse 

 temperature measurements with the resistance thermometer are so 

 accurate and so simple. 



From the point of view of thermometry it is important to know 

 what formula represents with a given accuracy the resistance of a 

 platinum wire for a certain range, and how many points must be 

 chosen for the calibration in this range. 



In Comm. N". 93 § 10 tlie conclusion has been drawn that between 

 O' and — 180° a quadratic formula cannot represent the observa- 

 tions more accurately than to 0^.15, and that if for that range a 

 higher degree of accuracy is required, we want a comparison with 

 the hydj-ogen thermometer at more than two points, and that for 

 temperatures below — 197° a separate investigation is required. In 

 the investigation considered here the temperatures below — 180° are 

 particularly studied; the investigation also embraces the temperatures 

 which can be reached with liquid hydrogen. 



It is of great importance to know wiiether the thermometer wdien 

 it has been used during a longer time at low temperatures would 

 retain the same resistance. We hope to be able later to return to 

 this question. Here we may remark that with a view to this question 

 the wire was annealed before the calibration. Also the differences 

 between the platinum wires, which w^ere furnished at different times 

 by Heraeus, will be considered in a following paper. 



§ 2. Investigations by others. Since the appearance of Comm. 

 N". 93 there has still been published on this subject the investigation 

 of Travers and Gwyer^). They have determined two points. They 

 had not at their disposal sufficient cryostats such as we had for 

 keeping the temperatures constant. About the question just mentioned : 

 how to obtain a resistance thermometer which to a certain degree 

 of accuracy indicates all temperatures in a given range, their paper 

 contains no data. 



^ 3. Modification in the arrangement of the resistances. The 

 variation of the zero of the gold wire, mentioned in Comm. N". 93 

 VIII, made us doubt whether the plates of mica between the metallic 

 parts secured a complete insulation, and also the movability of one of the 

 glass cylinders made us decide upon a modification in the construction 

 of the resistances, which proved highly satisfactory and of which we 



1) Travers and Gwyer. Z. f. Phys. Ghem. LII, 4, 1905. The wire of which 

 the calibration is given by Olszewski, 1905, Drude's Ann. Bd. 17, p. 990, is appa. 

 rently according to himself no platinum wire. (Gomp. also § 6, note 1). 



