414 On Light. 



is more than double that of air ; and much superior to that of 

 water. 



But since every substance ought to introduce into its combina- 

 tions, its peculiar character, and preserve in them, to a certain 

 degree, the force with which it acts on light, let us endeavour to 

 calculate, in this point of view, the refractive influence of the con- 

 stituents of a compound. From our knowledge of the extreme 

 tenuity of light, it is probable, that the influence of a moderate 

 chemical condensation, ought to affect its operations very slightly; 

 for, whether it be an ether or a corpuscular emanation, the ex- 

 cessive minuteness of its particles, compared to the distances be- 

 tween the molecules of bodies, ought to render the change of di- 

 stance among the latter, unimportant. Consequently, the re- 

 fracting powers of bodies ought to differ very little from those of 

 their elements, unless a very great degree of condensation has 

 taken place. 



Hence, if we multiply the proportions of azote and oxygen re- 

 spectively, by their refractive powers, we shall obtain products, 

 whose sums will coincide with the refractive power of the atmo- 

 sphere. Thus, 100 parts by weight of the atmosphere, consist 

 of azote 77*77+ oxygen 22*22. If we multiply each of these 

 numbers by the number representing the refractive power of the 

 body, and making a small correction for the carbonic acid pre- 

 sent, we shall have for the sum of the products I'OOOO. 



Ammonia, however, furnishes a more interesting example of 

 the application of these principles. 



The refractive power of hydrogen is , . . . 6*61436 



of azote .. 1*03408 

 of ammonia 2- 16851 



Let X be the weight of the constituent, whose refractive power 

 is . . . . . . .\ . . . . a 



y = 100 — a; = that whose power is . . . . If 



and call the refractive power of the compound . , c 



Then x = — — . In the present case, 



2-16851 — 1-03408 n ono jin/\ rv -rn-r 



^ = mMZmWH = 0-203 and 100 -x =0*797 = 

 the azote in 100 parts of ammonia; which may be regarded as 

 an approximation. The true proportions given by the equivalent 

 ratios are, 0*823 azote + 0.177 hydrogen. If the refractive 

 power of ammonia were 2-0218, then the chemical and optical 

 analysis would coincide. 



If we calculate on the above data, what ought to be the re- 

 fractive power of water, as a compound of 8 parts of oxygen + 

 1 hydrogen, we shall obtain the number 1*50065, which being 



multiplied 



