223 Dr, Brewster oji the Polarisation of Light, 
8,640,000 plates, the number by which light is polarised at 
an incidence of a single second. 
Thefrst column contains the number of plates in each parcel ; 
the second the angles of incidence at which each parcel pola- 
rises the transmitted light, calculated from the preceding 
formula, and extending to parcels below eight, and above 
forty- seven, which could not easily be made the subject of 
experiment; the third column contains the experimental results 
from which the law was deduced ; and the fourth exhibits the 
differences between the calculated and observed angles. The 
differences are all within the limits of error, and are singularly 
small when we consider the difficulty of observing the com- 
plete extinction of a luminous object, when the light by which 
it is formed has traversed a great number of plates. When 
the angle of incidence exceeds the angles of polarisation con- 
tained in the table, the pencil of light still emerges in a pola- 
rised state. 
