TABLE 200. 

 INDEX OF REFRACTION. 



Indices of Refraction of Gases and Vapors. 



193 



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

 temperature. More recent experiments confirm their conclusions. The formula is n t i = ^ ^ ~-> where 

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

 with temperature, and / the pressure of the gas in millimeters of mercury. 



SMITHSONIAN TABLES. 



