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Physics. — "On the measurement of ver;/ loio temperatures. XV. 

 Calibration of some platinum-resistance thermometers." By Prof. 

 H. Kamerlingh Onnes and J. Clay. Communication N°. 99'' 

 from the Physical Laboratory at Leiden. 



(Communicated in the meeting of June 29, 1907). 



§ 1. Introduction. The investigation on the variation of the 

 resistance of metals (pure ones and those with known admixtures) 

 set on foot many years ago (see Comm. N°. 77 § J These Proc. 

 Febr. 1902) at Leiden, comprises besides the determination of the 

 galvanic resistance of conductors made of the different metals, also 

 the determination of the expansion for each of these metals. We 

 have only little advanced as yet with the latter part of this investi- 

 gation, the expansion has only been investigated for platinum, which 

 was chosen as standard metal, and then only down to — 182°. l ) 

 We hope shortly to publish a Communication on the expansion 

 down to — 252° C. For the present, however, the knowledge of 

 this expansion is not yet of much importance for the investigation 

 of the variation of the specific resistance with the temperature. 

 When in this investigation we descend to very low temperatures, 

 the correction for the expansion becomes so small compared with 

 the disturbance in consequence of other influences which are still 

 further to be investigated, that we may disregard it for the moment. 2 ) 



The investigation consists then in the calibration of different resi- 

 stance thermometers. The wires treated in this Communication being 

 chiefly of importance to us as resistance thermometers, we have 

 inserted their calibration in this series. 



') In Comm. N°. 85 (These Proc. April 1905) it was observed for the first time 

 that in order to represent the expansion of glass from — 180° to 0° a for- 

 mula of the second degree with other constants was required than for the range 

 from D to + 100\ We found this confirmed in Comm. N°. 95'-» (These Proc. 

 Sept. '06), and also applicable to platinum, for which a formula of the third 

 degree, as we gave one for glass, proved necessary between — 180 and +100°. 

 Afterwards (Dec. '07) Scheel, who was at first (Zeitschr. f. Instr.k. April '06) of 

 opinion that a formula of the second degree could be found for platinum between 



— 190° and -f- 100 ', come to the same opinion as we, and gave the three constants for 

 platinum. Our formula of the second degree for platinum between 0° and — 180° quoted 

 by Scheel was used by us to prove, that for platinum between —ISO 3 and +100° 

 a formula of the second degree is not sufficient, but that a formula of the third 

 degree is required. In order to show this with given values at + 100°, 0° and 



— 190° observations at a temperature about halfway between 0° and — 190°, as 

 our — 87°, are more suitable than observations at a temperature between 0° and 

 + 100°, as those by Scheel at + 56°. 



2 ) Here it is left entirely undecided whether the variation of the resistance with 

 the temperature is not in close connection with the expansion. 



