30G 
DR. BREWSTER ON THE PHENOMENA AND LAWS 
Steel. — Angle of Incidence 68°. 
Azimuth to 
Right. 
Complement of Angle of Resto- 
ration by Second Plate. 
Azimuth to Complement of Angle of Resto- 
Left. ration by Second Plate. 
0 
0 
o 
... 11 
O 
0 . . 
o 
11 
iii . 
... 24 
ni . . 
10 
22i . 
• . . 24^ 
22i . . 
9 
33f . 
. . . 25i 
33f . . 
9f 
45 
• . . 26* 
45 . . 
1 1* 
56i . 
. . . 25§ 
56i . . 
15 
... 20 
m ■ • 
18 
78f • 
... 21 
78f - . 
20 
90 
... 22 
90 . . 
22 
By comparing these results with those obtained from 
steel at 75°, and with 
the observations already made on the 
passage of the ellipse 
into a straight 
line, the following results may be deduced. 
Angle of Incidence on 
Ratio of Semiaxes 
Character of the 
Position of the greater Axis 
first Steel Plate. 
of the Ellipse. 
Ellipse. 
of the Ellipse. 
o 
0 . . 
O 
0 
O 
: 90 
Straight line. 
. Azim. 90° and 270° 
68 . . 
9 
: 26 
Ellipse . . 
. betw. 45° and 56° 
to R. 
75 . . 
12 
: 22 
Ellipse . . 
45° 
to R. 
80 . . 
ql 
: 26 
Ellipse . . 
. 22i° 
to R. 
90 . . 
0 
: 90 
Straight line. 
0 
Hence it is obvious that the major axis of the ellipse is 45° + <p R to the 
right of 0° of azimuth, <p being computed from the formula 
tan <p — 
cos (i + i') 
cos (* — i'Y 
There is a deviation at the incidence of 68° and 80° of some amount, but still 
it is scarcely without the limits of the errors of observations when common light 
is used. In strong lights the coincidence will doubtless be more perfect. 
The best method of determining the position of the major axis, is to place the 
second plate at such an angle to the ray received from the first, that it may 
exceed by two or three degrees the angle of restoration in azim. 0°. Hence if 
we turn the second plate round the ray into all azimuths from 0° to 90° in the 
right hand quadrant where the greater axis lies, it must come into two azi- 
muths where the restoration takes place at the same incidence. The comple- 
