442 Dependence of Refractive Index on Temperature. [Feb. 26,. 



100 c C. The method used was the well-known one of Jamin, 

 but special precautions were taken to obtain accuracy, and to be 

 sure that the gas had not changed in composition during the various 

 changes of pressure and temperature to which the containing tube& 

 were subjected. An accuracy of about one part in 600 has been 

 obtained. 



The results are briefly shown in the following table, and it will be 

 observed that the temperature coefficients obtained are substantially 

 less than those obtained by Mas cart . 



Absolute Value of (i for the D line at 760 mm, and C C. 



Observer. 



Air. 



Hydrogen. 



Carbon 

 dioxide. 



Ammonia. 



Sulphur 

 dioxide. 



Mas cart 



1 -0002927 



1 -000294 

 1 -0002928 

 ±3 



1 -000139 

 1 -000139 

 1 -000143 

 1 -000138 

 1 -0001407 

 ±15 



1-000454 



1 -000449 

 1 -000449 

 1 '0004510 

 ±5 



1 -000379 

 1 -000373 



1 -000385 

 1 -0003793 

 ±5 



1 -0007038 



1 -000686 1 

 1 000665 

 1 -0006758 

 ±4 



Temperature Coefficients of Eefractive Index. 



Coeffi. of vol. expansion . 

 Mascart 



Air. 



Hydro- 

 gen. 



Carbon 

 dioxide. 



Ammonia. 



Sulphur 

 dioxide, i 



0-00367 

 -003S2 

 -00360 

 ±3 



-00366 

 -00378 

 -00350 

 ±3 



-00371 

 -00406 

 0-00380 

 ±3 



0-00382? 



-00390 

 ±3 



-00390 . 

 0-00460 j 

 0-00416 ! 

 ±2 | 



1 





