( 209 ) 



have availed ourselves alread}' in the regulation of the temperatures 

 in the investigation mentioned in Comm. N". 94^^. 



A difficulty adheres to this arrangement which we cannot pass by 

 unnoticed. Owing to the manner in which this thermometer has been 

 mounted it cannot be immersed in acid. Therefore an apparatus 

 consisting entirely of platinum and glass remains desirable. A similar 

 installation has indeed been realized, A description of it will later 

 be given. The figures given here exclusively refer to the thermometer 

 described in Comm. N°. 94^ (p. 210). 



Care has been taken that the two pairs of conducting wires were 

 identical. Thus the measurement of the resistance is performed in 

 a much shorter time so that both for the regulation of the tem- 

 perature in the cryostat and, under favourable circumstances, for the 

 measurement the very same resistance thermometer can be used. 



§ 4. The temperatures. 



The temperatures were obtained in the cryostat, described in Comm. 

 N". 94^^, by means of liquid methyl chloride —39°, —59°, —88°, of 

 liquid ethylene -103^ —140°, —J 59°, of liquid oxygen —182°, 

 — 195\ —205°, —212°, —217°, by means of liquid hydrogen 

 — 252° and — 259°. The measurements were made with the hydrogen 

 thermometer as mentioned in § 1. 



§ 5. Results for the platinum wire. These results are laid down 

 in table I (p. 210). 



The observations marked with [ ] are uncertain on account of the 

 cause mentioned in Comm. N°. 95^^ § 10 and are not used in the 

 derivation and the adjustment of the formidae. For the meaning of 

 W — Raj in the column "remarks" I refer to § 6. 



^ 6. Representation by a formula. 



a. We have said in § 1 that the quadratic formula ') was insuffi- 

 cient even for the range from 0° to — 180°. 



If a quadratic formula is laid through —103° and — 182°, we 

 find : 



-) The correction of Gallendar, used at low temperatures by Travers and 

 GwYER, Z. f. Phys. Ghem. LII, 4, 1905 comes also to a quadratic formula. 

 Dickson's quadratic formula, Phil. Mag. June 1898, is of a different nature but 

 did not prove satisfactory either; comp. Dev^ar Proc. R. Soc. 64, p. 227, 1898. 



The cahbration of a platinum thermometer through two fixed points is still 

 often applied when no hydrogen thermometer is available (for instance Bestelmeyer 

 Drude's Ann. 13, p. 9G8, '04). 



