165 
428. Neither does the supposed refractive power 
of oxygen give any support to this doctrine; for, 
from the experiments of M. M. Biot and Arrago, it 
appears, that hydrogen, in this respect, exerts the 
greatest force ; and oxygen, on the contrary, is one 
of the bodies that has the least refractive power. 
Hence it is from the hydrogen they contain, that wa- 
ter, oil, and other substances, refract light in a ratio 
so much surpassing their density *. These results, 
therefore, accord perfectly with the facts observed, 
and the conjectures submitted by Newton, respecting 
the great refractive power of inflammable bodies ; 
but they yield no support to the opinion entertained 
of the predominance of this property -in oxygen. 
429. With respect, also, to vegetable bodies, it 
is not easy to conceive how the presence of oxygen 
should produce their various colours. Except the 
pure bases of the alkalis, the earths, and the metals, 
almost every substance in nature appears, from Mr 
Davy's researches, to contain a small portion of oxy- 
gen ; so that, in every change of composition which 
bodies undergo, oxygen must be more or less enga- 
ged. The universality of its presence, however, taken 
in connection with the ever-varying proportions in 
which it exists in bodies, and the infinite variety of 
shades and colours which these bodies present, fur- 
nishes arguments against the idea of its acting as the 
colouring principle of matter : nor does it readily 
appear why the oxygen, more than any other ingre- 
dient of the body, should give rise to the formation 
Hauy's Traite de Phys. vol. ii. p. 18 
