On Polarization of Light by Reflexion. 287 
as I know there have been no absolute measures taken of the quan- 
tity of polarized light at different incidences, yet we are fortunately 
in possession of a set of experiments by M. Arago, who has as- 
certained the angles above and below the polarizing angle at which 
glass and water polarize the same proportion of light. In no case 
has he measured the absolute quantity of the polarized rays; but the 
comparison of the values of Q at those angles at which he found them 
in equal proportions, will afford a tést of the accuracy of the formu- 
la. This comparison is shown in the following table, in which col. 1. 
contains the angles at which the reflecting surface polarizes equal 
proportions of light; col. 2. the values of g or the inclination of the 
planes of polarization; and col. 3. the intensities of the polarized 
light computed from the formula. z 
Angles of Inclination of Planes of Proportion of i 
Incidence i. Polarization to M N, or. Polarized light or Q. 
BIo Bake 20 12 
; 82° 48” ; 
poem: 7 of is. ae. 
‘ Biggs BB Bee BOAT es oe 9:08 
2a te ee” ak eee 
ei a 
«8.596 gg eee 
: 6 sr te a ee 
wanes tm 4.476 1 OE 1 
The agreement of the formula with experiments made with as 
great accuracy as the subject will admit must be allowed to be very 
satisfactory. ‘The differences are within the limits of the. errors of 
observation, as appears from the following table : 
Deviations from Part of 
i hole Light. 
Glass: No. 1. 0.0065 . . . = = yf 
No: 2: 0.0862 0 = 
Nos 0018 OO 
Water: No. 4; 0.0166. *. 2 © as 
M. Araco has concluded, from the experiments above stated, that 
equal proportions of light are polarized at equal angular distances from 
the angle of complete polarization. Thus in Glass No. 1. the mean 
of 82° 49/ and 24° 19’ is 53° 33’, which does not differ widely from 
the maximum polarizing angle, or 55°, which M. Anaco considers as 
