AND ON THE ACTION OF LIGHT ON BODIES. 435 
mentary colours would be called in to aid the explanation ; it 
would be said, that with the primary impression of any colour, 
the complementary is formed after some time, which combines 
with the primary colour and forms white. This, however, can 
hardly be called an explanation ; for if we consider colour accord- 
ing to our ideas as a determinate number of oscillations of the 
ether in a certain time, we cannot attach any precise meaning 
to such an hypothesis. The theory of the action of comple- 
mentary colours on the eye, a subject which will be treated of 
more fully in the next part of this treatise, seems to me to have 
been only an invention of necessity, in order to bring under it 
the subjective colours, while, according to our view of the subject, 
these pheenomena become easily explicable without the assistance 
of a peculiar vital principle. The general opinion, and more par- 
ticularly in France, at present entertained, is that there are peculiar 
chemical rays which are different from the luminous ones. My 
hypothesis as to the process of vision could not possibly stand, 
if such a theory were admitted as correct; but as far as I know 
there is nothing in favour of this hypothesis except the exist- 
ence of non-luminous, so-called chemical rays. I am not aware 
of any other phenomenon which tends to support it, and cer- 
tainly no one will seriously adduce as such the experiments on 
the passage of chemical rays through certain bodies. The best 
way of determining whether there is any necessity for making a 
distinction between chemical and luminous rays, appeared to me 
to be the examination of the action of polarized light on sensi- 
tive bodies. I have never observed any appearance of this kind 
in the most varied experiments ; and if we allow the existence of 
chemical rays, we must at least admit that, as far as regards 
polarization and interference, they follow the same laws as the 
luminous rays. By means of Iceland spar I was enabled to ob- 
tain images similar in every respect to those of Daguerre. 
For this purpose I placed before the lens of the camera ob- 
scura (the lenses are best if with short focal distances) an achro- 
matic prism of calc-spar, and adjusted it so that both images of 
the object were apparent. The best object that can be chosen 
is a statue, for if buildings are taken the parts overlap. When 
achromatic calc-spar is used, only the ordinary image is colour- 
less, the other is furnished with coloured edges, which, however, 
in my experiments did not injure the clearness of the image. 
Moreover, I obtained a representation of the annular system of 
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