Table 1 98. 



INDEX OF REFRACTION. 



Indices of Refraction of Oases and Vapors. 



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 »<— i = , j-n/'^"6^' where 

 «, is the index of refraction for temperature t, «» for temperature zero, o the coefficient of expansion of the gas 

 with temperature, and/ the pressure of the gas in millimetres of mercury. Taking the mean value, for air and 

 white light, of «o — • as 0.0002936 and o as 0.00367 the formula becomes 



.0002936 _ P .0002895 P 



' I-)-. 00367/ 1.0136X10* 1 4- .00367 10*' 



where P is the pressure in dynes per square centimetre, and t the temperature in degrees Centigrade. 



Smithsonian Tables. 



190 



