296 On the Affinities of Bodies for Light, 
Thus, according to Lavoisier, oil of olives is composed 
of 0°21 of hydrogen (in weight), and 0°79 of carbon.. But 
on combining according to these relations the refractive 
force of hydrogen as it results from the observations of the 
authors of the memoir, and that of carbon, as concluded 
from the trial made on carbonic acid, we find the refractive 
force of the oil of olives to be = 250, that of the air being 1. 
But Newton’s observations give 2°73 for the refractive power 
of oil of olives. The difference between calculation and ob- 
servation is, therefore, scarcely one-ninth of the total value ; 
and it takes place in circumstances which condensation tends 
to explain. The following is a verification sufficiently satis- 
factory : 
The analysis Bs alcohol, also made by Lavoisier, pre- 
sents another mean for athe a similar proof. This li- 
quid is composed, according to him, of 0°544 of oxygen, 
0°166 of hydrogen, and 0:29 of carbon. According to these 
proportions, the refractive power of alcohol is found upon 
calculation to be = 1:94, that of the air being 1. But the 
experiments of Newton give = 2°23 for alcohol. The dif- 
ference is one-eighth of the total amount ; but the difference 
of the results; may be explained by a condensation of the 
change from the gaseous to the liquid state. Jn the last 
place, the chemical analysis of gum given by Messrs. Four- 
croy and Vauquelin admits of trying the refractive analysis 
~ of the same solid as a verification of this new process. Ac- 
cording to these chemists, gum is composed of 0°6538 of 
oxygen, 0°1154 of hydrogen, and 0:2308 of carbon. . From 
this the refractive power of gum deduced from calculation 
would be = 1°63; according to Newton it is = 1°89, The 
difference of abebt one-seventh is again, in some > measure, 
favourable to the explanation given. 
The want of an exact analysis of other substances into 
which carbon enters, does not allow us to push the parallel 
of the two methods any further. But we may say that in 
these very substances the refractive powers observed place 
them in the order indicated by the combined influence of 
their elements. Thus the refraction is strongest where hy-: 
drogen 
