408 A. L. Day and J. K. Clement— Gas Thermometer. 



If this somewhat circumstantially selected system does not 

 at the moment appear to confront any insuperable obstacle, 

 many and insidious difficulties have been encountered in the 

 course of its development. One has only to examine the 

 determinations of the same temperature made by different 

 observers, all using substantially this method, to become con- 

 vinced that some serious work still requires to be done to clear 

 up the present uncertainty. The melting point of gold is 

 given by Barus (1892) at 1092° ; by Holborn and Wien (1895), 

 1072°; Holborn and Day (1900), 1063-5° ; by Jacquerod and 

 Perrot (1905), 1067*2°; by Day and Clement (preliminary, 

 1907), 1059*1°. For the moment it is sufficient merely to call 

 attention to these differences in the results which have been 

 obtained, and to reserve detailed comment upon them for a 

 subsequent part of the paper. Suffice it to say that both Hol- 

 born and Day at the close of their work (1900) entertained the 

 positive opinion that the discrepancies had occurred in the 

 experimental details and were not chargeable to an oversight 

 in any of the more fundamental relations involved. 



With this prevailing idea in mind — that the general relations 

 are already satisfactorily worked out and that the problem 

 remaining is therefore primarily an experimental investigation, 



(1) to increase the absolute accuracy of the measurements, and 



(2) to extend their range — Prof. Holborn at the Peichsanstalt 

 and the authors at the Geophysical Laboratory took up the gas 

 thermometer again in 1904. The details were for the most 

 part independently planned and the work has been indepen- 

 dently carried out. In a research which offers so many 

 technical difficulties, two independent plants were obviously 

 better than one. In so far as a division of labor was 

 attempted, Prof. Holborn entered at once upon the more daring 

 undertaking, namely, to increase the range of measurement. 

 He built a bulb of pure iridium in the hope that it might prove 

 possible to make continuous gas thermometer measurements as 

 far as the melting point of platinum. For this work the 

 errors of observation were allowed to remain large, larger in 

 fact than they had been in the joint work of Holborn and Day 

 in 1900. The undertaking was entirely successful and yielded 

 very satisfactory measurements up to about 1600°,* the error 

 for the new portion of the gas scale (from 1150° on) being 

 about 10°. 



Our work was for the moment restricted to 1200° in an 

 effort to eliminate or materially to diminish the errors which 



* Temperaturmessungen bis 1600° mit dem Stickstoffthemionieter u. mit 

 dera Spektralphotonietei*, Sitzungsber. Berl. Akad. xliv, p. 811, 1906 ; Ein 

 Vergleichung der Optischen Temperaturscala mit dem Stickstoffthermome- 

 ter bis 1600°, Ann. d. Phys. (4), xxii 3 p. 1, 1907. 



