128 Dr. Brewster on the laws which regulate the 
the fourth column the differences between the calculated and 
observed angles, and in the fifth column the calculated angles 
of polarisation for the second surfaces of the bodies subjected 
to experiment. 
Table containing the calculated and observed polarising angles for 
various bodies. 
Names of the Bodies.. 
Calculated po- 
larising angles 
for the first 
surface. 
Observed pola- 
rising angles 
for the first 
surface. 
1 Difference be- 
tween the calcu- 
lated and ob- 
served angles. 
Calculated po- 
larising angles 
for the second 
surface. 
© 
/ 
// 
O 
0 
0 / 
// 
Air - - - - - 
45 
O 
32 
45 or 47 
44 59 28 
Water - - - - 
53 
11 
0 
5 2 ° 
45 ' 
0° 
26' — 
3 6° 
49 ' 
Fluor spar - - - 
55 
9 
0 
54 
50 
O 
19 — 
84 
5 i 
Obsidian - 
5 6 
6 
0 
5 ^ 
3 
0 
3 — 
33 
54 
Birdlime - - - - 
& 
40 
0 
56 
4 « 
0 
6 + 
33 
20 
Sulphate of lime - 
5*5 
45 
0 
56 
28 
O 
17 — 
33 
15 
Rock crystal - - 
5 6 ' 
58 
0 
57 
22 
O 
24 + 
33 
2 
Opal coloured glass 
58 
33 
0 
58 
1 
O 
3 2 — - 
31 
2 7 
Topaz - - - - 
58 
34 
0 
58 
40 
O 
6 + 
31 
26 
Mother of pearl 
58 
50 
0 
58 
47 
O 
3 — 
3 i 
10 
Iceland spar 
58 
51 
0 
58 
23 
O 
98 — 
3 i 
9 
Orange coloured glass 
59 
28 
0 
59 
12 
O 
16 — 
30 
32 
Spinelle ruby - - 
60 
25 
0 
60 
16 
0 
9 — 
2 9 
35 
Zircon - - - - 
6 3 
0 
0 
6 3 
8 
0 
8 + 
27 
0 
Glass of antimony 
64 
3 ° 
0 
64 
45 
0 
15 + 
2 5 
3 ° 
Sulphur - - - - 
6$ 
45 
0 
64 
10 
0 
25 + 
26 
15 
Diamond - 
68 
1 
c 
68 
2 
0 
1 + 
21 
59 
Chromate of Lead 
68 
3 
0 
67 
42 
0 
21 — 
21 
56 
The coincidence between the calculated and observed an- 
gles, as shown in the preceding Table, must appear very re- 
markable to those who are aware of the difficulty of measuring 
