REFRACTIVE INDEX OF GASES ON TEMPERATURE. 
455 
The difference between tire temperature coefficient of refraction and tlie coefficient 
of expansion has naturally attracted my attention ; hut I do not propose to discuss 
the matter theoretically in this paper, mainly because I am now taking up experi¬ 
ments on tlie temperature coefficients of the dielectric constants, whicli I hope will 
give me a more complete basis for generalization. 
In conclusion, I wish to express my great obligation to Professor Tnoii.soN for 
having placed the appliances of the laboratory at my disposal, and for his kind interest 
in what has necessarily been a very tedious work. 
PEEL. 
