292 



Table 348. 

 INDEX OF REFRACTION. 



Indices of Rsfraotlon ol Qases and Vapors. 



A formula was given by Biot and Arago expressing the dependence of the index of refraction of a gas on pressure and 



temDevature. More recent experiments confirm their conclusions. The formula is «, — i = — ; •-— ' where 



■^ I -f-at 760 



«i is the index of refraction for temperature /, Hq for temperature lero, a the coefficient of expansion of the gas 



with temperature, and/t the pressure of the gas in millimeters of mercury. For air see Table 349. 



Smithsonian Tables. 



