292 



TABLE 348. 

 INDEX OF REFRACTION. 



Indices of Refraction of Gases and Vapors. 



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



0_! p 

 temperature. More recent experiments confirm their conclusions. The formula is n t i = /"A"' ere 



n t is the index of refraction for temperature /, for temperature zero, a the coefficient of expansion of the gas 

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



SMITHSONIAN TABLES. 



