( 182 ) 



RoTHE^) could only arrive at an indirect comparison with the hydrogen 

 thermometer. He compared his thermo-elements constan tin-iron at 

 • — 79° with the alcohol thermometer which Wiebp: and Böttcher *) 

 had connected with the gas thermometer and at — lOl'' with a 

 platinum-resistance thermometer which at about the same tempera- 

 ture had been compared with the hydrogen thermometer in the 

 Phys. Techn. Reichsanstalt by Holborn and Dittenberger '). 



The thermostat left much to be desired ; temperature deviations 

 from 0^.4 to O'^.l occurred within ten minutes (comp. for this § 7). 

 As RoTHE confined himself to two points, he had to rest content with 

 a quadratic formula and he computed the same formula as Holborn 

 and WiEN. 



From the values communicated for other temperatures we can 

 only derive that the mutual differences between the deviations of the 

 different thermo-elements constantin-iron and constantin-copper from 

 their quadratic formulae could amount to some tenths of a degree. 

 Nothing is revealed with regard to the agreement with the hydrogen 

 thermometer. This investigation has no further relation to the problem 

 considered here. 



b. Among the thermo-elements of other composition we mention 

 that of Wroblewski "), who compared his new-silver-copper element 

 at + 100° (water), — 103° (ethylene boiling under atmospheric pressure) 

 and — 131° (ethylene boiling under reduced pressure) with a 

 hydrogen thermometer and derived thence a cubic formula for t. 

 He tested it by means of a determination of the boiling points of 

 oxygen and nitrogen and found an agreement with the hydrogen 

 thermometer to within 0°.l. As, however, Wroblewski found for 

 the boiling point of pure oxygen at a pressure of 750 m.m. —181°. 5, 

 no value can be attached to the agreement given by him. 



Dewar's ^) investigation of the element platinum-silver was for the 

 time being only intended to find out whether this element was suited 

 for measurements of temperatures at — 250° and lower (where the 

 sensitiveness of the resistance thermometer greatly diminishes), and 

 has been confined to the proof that this really was the case. 



c. To our knowledge no investigation has therefore been made as 

 yet, which like that considered in our paper, allows us to judge in 



') Ztschr. fur Instrumentenk. Bd. 22 p. 14 and 33. 1902. 

 2) , , „ Bd. 10 p. 16. 1890. 



5) Drude's Ann. Bd. 6 p. 242. 1901. 



*) Sitzungsber. Ac. Wien Vol. 91. p. 667. 1885. 



6) Proc. R. S. Vol. 76, p. 317. 1905. 



