280 On Polarization of Light by Reflexion. 
principal section in the plane of reflexion, and viewing through it 
- the images A and B at 80° of incidence. As the axis of A is in- 
-clined 33° to MN or the section of the rhomb, the ordinary image 
of it will be much brighter than the extraordinary image, the inten- 
sity of each being in the ratio of cos? @ to sin? 9, 9 being the an- 
gle of inclination, or 33° in the present case. In like manner the 
ordinary image of B will be in the same ratio brighter than its ex- 
traordinary image, that is, by considering A and B in’a state of su- 
perposition, the extraordinary image of a pencil of light reflected at 
80° will be fainter than the ordinary image in the ratio of sin? 33° 
to cos? 33°, But this inequality in the intensity of the two pencils 
is precisely what would be produced by a compound pencil, part of 
which is polarized in the plane of reflexion, and part of which is 
common light. When Matus, therefore, and his successors analy- 
sed the pencil reflected at 80°, they could not do otherwise than 
conclude that it was partially polarized, consisting partly of light po- 
larized in the plane of reflexion, and partly of natural light. The 
action of successive reflexions, however, afforded a more precise 
means of analysis, in so far as it proved that the portion of what was 
deemed natural light ‘had in reality suffered a physical change, 
which approximated it to the state of polarized light; and we now 
see that the portion of what was called polarized light, was only what 
may be called apparently polarized ; for though it disappears, like po- 
larized light, from the extraordinary image of the analysing prism, yet 
there is not a single particle of it polarized im the plane of reflexion. 
These results must be admitted to possess considerable interest in 
themselves; but, as we shail proceed to show, they lead to conclu- 
sions of general importance. ‘The quantity of light which disap- 
pears from the extraordinary image, is obviously the quantity of light 
which is really or apparently polarized at the given angle of incidence; 
and if we admit the truth of the law of repartition discovered by Ma- 
Lus, and represented by Poo=Po cos? 9, andPoe=Po sin? g, and if 
we can determine 9 for substances of every refractive power, and 
for all angles of incidence, we may consider as established the 
mathematical law which determines the intensity of the polarized 
pencil, whatever be the nature of the body which reflects it,—what- 
ever be the angle at which it is incident,—whatever be the number of 
reflexions which it suffers, and whether these reflexions are all made 
from one substance, or partly from one substance and partly from 
another. 
