312 
DR. BREWSTER ON THE PHENOMENA AND LAWS 
Hence we are led to the important conclusion, that the pencil which enters 
the metal follows the changes of polarization of the partially reflected pencil, 
which is regulated by the same law as in transparent bodies. 
It now became interesting to examine the effect produced by the joint action 
of the metal, and an equivalent crystal, in changing the plane of polarization 
of the restored ray. The following are the results with different metals at the 
maximum polarizing angle. 
Metals. 
Position of the Plane 
of Polarization. 
Rotation 
effected. 
Silver (pure) . 
. . . + 42 
o 
. . 3 
Copper . . . . 
. . . +36J . . 
GO 
Mercury . . . . 
... -f 35 
. . 10 
Platina . . . 
. . . + 34 
. . 11 
Speculum metal . 
... -f 32 
. . 13 
Steel 
. . . +30i . . 
• • 14* 
Lead 
. . . + 26 
. . 19 
Galoena . . . 
• • • +17i • • 
. . 2 
These metals follow the same order in their action upon the plane of polari- 
zation that they hold in the Table in page 294, though in reference to the rota- 
tion actually produced in both cases the order is inverted. 
The preceding Table points out in a very instructive manner the difference 
between the action of a metallic surface and an equivalent crystallized film. 
When two metallic surfaces act together, the plane of polarization of the 
restored ray is invariably thrown beyond the plane of reflexion ; whereas in 
the combination of a crystallized film with a metallic surface, the same plane 
never reaches the plane of reflexion, the plane having always a negative posi- 
tion in the former case, and a positive one in the latter. Thus in two reflexions 
from silver at 73°, the primitive ray polarized + 45° has its plane of polariza- 
tion changed into — 39° 48', whereas in the combination of one reflexion from 
silver with the crystallized film, the plane is changed only into +42°. 
In order to determine the law of the metallic action at different incidences 
and with different numbers of reflexions, I interposed between the eye and the 
metal, which was silver, a plate of calcareous spar, which exhibited its tiniaxal 
system of rings. 
