( 181 ) 



each iiulividually with two gas thermometers and also with each 

 other, wliile the deviation of the gas thermometer would be determined 

 by means of a differential thermometer '). Nitrogen liad originally 

 been chosen by the side of hydrogen, afterwards nitrogen Las been 

 replaced by helium. Because all these measurements have often 

 been repeated on account of constant improvements, only those figures 

 have been given which refer to the gold- and the platinum-resistance 

 thermometer ^), and these, for which others will be substituted in 

 Comm. X^ 95^^, are only of interest in so far as they show that the 

 method followed can lead to the desired accuracy. The results obtained 

 with regard to the above-mentioned thermo-element do not yet satisfy 

 our requirements in all respects; yet all the same it appeared desirable 

 to publish them even if it was only because the temperature deter- 

 minations for some measurements, which will erelong be discussed, 

 have been made with this thermo-element. 



§ 2. Comparisons made by other observers. 



a. Constantin-iron elements have been compared with a hydrogen 

 thermometer only by Holborn and Wien ^) and Ladexburg and 

 Krügel ^). The calibration of the two former investigators is based 

 on a comparison at two points viz. in solid carbon dioxide and 

 alcohol (for which — 78°. 3 is given) and in liquid air (for which 

 they found — 189M). They hold that the temperature can be 

 represented by the formula 



t = aE -\- bE' 



and record that at an obserxation for testing purpose in boiling 

 oxygen ( — 183°. 2 at 7GÜ m.m. mercury pressure) a good harmony 

 was obtained. 



Ladexburg and Krügel deem Holborn and Wien's formula unsatis- 

 factory and propose 



t = aE -I- bE' + cE\ 



They compare the thermo-element with the hydrogen thermometer 

 at 3 points, viz. solid carbon dioxide with alcohol, boiling ethylene 

 and liquid air. As a control they have determined the melting point 

 of ether ( — 112°) and have found a deviation of 1 deg. With this 

 they rest satisfied. 



1) Comp. comm. N°. 94''. (Idem June 1905). 



2) Gorap. comm. N'\ 93. (Idem Oct. 1904). 



3) Silz.ber. Ac. Berlin. Bd. 30, p. G73, 189G, 'and Wied. Ann. Bd. 59, p. 213. 1896. 

 *) Ghem. Ber. Bd. 32, p. 1S18. 1899. 



13 

 Proceedings Royal Acad. Amsterdam. Vol. IX. 



