DR. BREWSTER ON THE PHENOMENA AND LAWS 
324 
traordinary image at any angle a, because this must depend on the relative 
intensities of the pencils by whose interference the elliptical polarization is 
produced. In silver these pencils approach to equality, but in steel and other 
metals they are very unequal. 
Having thus shown how to determine the phenomena of elliptic polarization 
for any angle of incidence, for any number of reflexions, and for homogeneous 
light of any colour, I shall conclude this paper with some observations on a 
very remarkable anomaly which has presented itself in the course of this 
inquiry. 
The phenomena which have been described, indicate very clearly that the 
angle of maximum elliptic polarization for one reflexion, or the angle of resto- 
ration after two equiangular reflexions, is the maximum polarizing angle of the 
metal, and consequently that its tangent is the index of refraction, as shown in 
the following Table*. 
Names of Metals. 
Angles of Maximum Polarization. 
Index of Refraction. 
Grain tin .... 
. . . 78 30 . . . 
. . . 4.915 
Mercury 
... 78 2 7 . • • 
. . . 4.893 
Galsena 
. . . 78 10 . . . 
. . . 4.773 
Iron pyrites .... 
o 
CO 
VN. 
. . . 4.511 
Grey cobalt .... 
. . . 76 56 . . . 
. . . 4.309 
Speculum metal . . 
. . . 76 0 . . . 
. . . 4.011 
Antimony melted . . 
. . . 75 25 . . . 
. . . 3.844 
Steel 
. . . 75 0 . . . 
. . . 3.732 
Bismuth 
. . . 74 50 . . . 
. . . 3.689 
Pure silver .... 
. . . 73 o . . . 
. . . 3.271 
Zinc 
. . . 72 30 . . . 
. . . 3.172 
Tin plate hammered . 
. . . 70 50 . . . 
. . . 2.879 
Jewellers’ gold . . 
. . . 70 45 . . . 
. . . 2.864 
' This Table completely proves that the refractive index of metals cannot he deduced from their 
reflective power; for silver, which surpasses them all in reflective power, stands very low in refractive 
power. Mr. Herschel has noticed the difference between the indices of refraction deduced by these 
two methods in the case of mercury, which he makes 5.829 as given by its reflective power, and 
Ll<> as given by its polarizing angle. lie mrdees the index for steel 2.85. When we consider that 
mi ' als reflect the light that enters their substance, it must be obvious that the quantity of light which 
