230 Dr. Brewster on the laws oj polarisation , &c. 
\ 
It would occupy too much room to detail the various prac- 
tical methods to which I have been obliged to resort in 
determining the position and inclination of the diameters of 
no polarisation. In some crystals this process is sufficiently 
simple, as in topaz, mica, nitre, talc, mother of pearl, prussiate 
of potash &c. but in other crystals it is extremely difficult, 
particularly when the angle of inclination is great, and when 
the specimen is small and its crystalline form indistinct. 
The following table contains this angle for 49 crystals. 
The measures were taken with great care, but some of them 
are only estimated, and others will admit of correction by the 
use of better specimens than those I was able to procure. 
Table of the inclination of the resultant axes of forty nine 
crystals. 
Sulphate of nickel, certain speci- 
25 Sugar 
5° 
0 
mens 
3 
0 
Sulphate of strontites 
5° 
2 
Carbonate of lead 
- 5 
*5 
Murio-sulph. magn. and iron 
51 
16 
Nitrate of potash 
5 
20 
Sulph. ammon. and magnes. 
51 
22 
Talc 
- 7 
24 
Phosphate of soda 
55 
20 
Mother of pearl 
1 1 
28 
30 Sulphate of lime 
60 
0 
Hydrate of barytes 
>3 
18 
Oxynitrate of silver 
62 
16 
Mica,certain specimens, about 14 
0 
Feldspar - 
63 
0 
Arragonite 
18 
18 
Topaz - 
65 
0 
Prussiate of potash 
19 
34 
Sulphate of potash 
67 
0 
Cymophane 
27 
5 i 
35 Carbonate of soda 
70 
1 
Borax 
- 28 
42 
Acetate of lead 
70 
25 
Anhydrite 
28 
7 
Citric acid - 
70 
29 
Sulphate of magnesia 
37 
24 
Tartrate of potash 
7 1 
20 
— — — — - — barytes 
37 
42 
Tartaric acid 
79 
0 
Tincal - 
38 48 
40 Tartrate potash and soda - 
80 
0 
Nitrate of zinc, estimated 
at 
Carbonate of potash 
80 
3° 
about 
40 
0 
Kyanite 
81 
48 
Stilbite 
41 
42 
Hyper-oxymur. potash 
82 
0 
Sulphate of nickel 
42 
4 
Muriate of copper 
84 30 
Carbonate of ammonia 
43 
24 
45 Epidote, about 
87 
0 
Mica ... 
45 
0 
Peridot 
87 c6 
Lepidolite 
45 
0 
Crystallized Chelt.-salts 
88 
14 
Benzoate of ammonia 
45 
8 
Succinic acid,estimated at about 
190 
0 
Sulphate of zinc 
44 
28 
Sulphate of iron 
90 
0 
— — ammonia 
49 42 
