214- M. Dulorrg 1 s Researches on the 



The refractive power of air at 0°, and at m 76, being 

 known either from the astronomical observations of Delambre, 

 or by the direct measures of M. Biot and Arago, we may de- 

 duce from the preceding numbers the value of the absolute 

 refractive powers of all the above gases, as well as the indices 

 of refraction for the passage of light from a vacuum into each 

 of the gases. 



The refractive powers of simple or compound gases do not 

 seem' to have any necessary relation to the density. The ole- 

 fiant gas, for example, and the oxide of carbon, have nearly 

 the same density, but the refractive power of the first is near- 

 ly double that of the second. 



It has been long known, that, in comparing solids or li- 

 quids of a different nature, the refraction is not proportional 

 to the density, and hence it has been concluded that every 

 body exercises upon light an action depending on its own na- 

 ture. But the different capacities of bodies for heat related to 

 a unity of mass, had led to an analogous conclusion relative to the 

 attractions which were admitted between bodies and the mat- 

 ter of heat. But since, in calculating the capacities of each 

 particular molecule, it has been found that they were equal, 

 or in simple relations, it would not be surprising if the same 

 idea, applied to refractive power, would lead to the discovery 

 of very simple relations where none had been discovered. 



