Table 200. 193 



INDEX OF REFRACTION. 



Indices of Refraction of Qases and Vapors. 

 A fonnula 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^ — i^ 



3-.. ;» 



where 



+ ai 760 

 f!^ is the index of refraction for temperature /, rtg for temperature zero, a the coefficient of expansion of the gas 



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



Smithsonian Tables. 



