1830.1 
On the Polarization of Light. 
113 
venient to insert a table of Sir Isaac’s measurements, and follow it up witli an exam- 
ple or two of application. 
Order I. 
Order II. 
Order III. 
Order IV. 
Order V. 
Order VI. 
Order VII. 
Thickness of laminae in millionths 
of an inch. 
L 
l 
I 
{ 
{ 
Very black. 
Black, 
Blue, 
White, 
Yellow, 
Orange, 
Red, 
Violet, 
Indigo, 
Blue, 
Green, 
Yellow, 
Orange, 
Red, 
Scarlet, 
Purple, 
Indigo, 
Blue, 
Green, 
Yellow, 
Red, 
Blueish red, 
Blue green, 
Green, 
Yellowish green, 
Red, 
Greenish blue, 
Red, 
Greenish blue, 
Red, 
Greenish blue, 
J Reddish white, 
of air. 
of water. 
of glass. 
k 
0.33 
0.3i 
1 
0.75 
0.61 
2.4 
1.8 
1.5 
5.2 
3.8 
34 
7.1 
5.3 
4.6 
8 
6. 
5.2 
9 
6.7 
5.8 
11.2 
8.4 
7.2 
12.8 
9,7 
8.2 
. 14. 
10.5 
9. 
- 15.1 
11.3 
9.6 
16.3 
12.2 
10.4 
17 2 
13. 
11.2 
18.3 
13.7 . 
11.7 
19.6 
14 7 
12,6 
21 
157 
13.5 
22.1 
16.7 
14.2 
23.4 
17.5 
15.1 
25.2 
18.9 
16.2 
27.2 
20.3 
17.5 
29. 
21.7 
18.7 
32. 
24. 
20.6 
34 
25.5 
22. 
35.4 
26.5 
22.7 
36. 
27. 
23.2 
40.3 
.30.2 
26. 
. 46 
34,5 
29.6 
52.5 
39.4 
34. 
53.7 
44. 
33. 
65. 
48.7 
42. 
71 
53.2 
45.8 
77 
57.7 
49.6 
Rock crystal, mica and sulphate of lime differ very little from glass in the above 
scale. To apply this table to practice, suppose we fix upon the following five plates 
of mica for measurement. We place them succesively in the interposition- circle of 
our instrument, (figure 33,) bring their axis of cr 3 r stallization to the azimuth 45* 
from the plane of first reflection : — then gently incline them to the ray, by turn- 
ing the index of the horizontal circle below, and note down the series of colours, 
from which we find the Newtonian colour of the plate when uninclined, and the 
consequent Newtonian measurement, viz. 
No. 
Colour of O 
Colour ofE, 
Rising series of E, I Supposed I Thickness 
on inclining the micajNewtoniancolour’correspond^ 
1 
Orange, 
Bl. white, 
wli. or red. vio.iud. bl 
wh. of 1st order 
4 
2 
Bl. white, 
Orange wh- 
red. pur. bl. gr. or.1 
cr- yell. 1st order 
7.7 
red, viol. blue, j 
3 
Blue, 
Orange,, 
scr. red, pur. hi. gr. 1 
orange, 2d order 
27.2 
yell, red, blue, J 
4 
Red, 
Green, 
green, 3d order 
2.5 
5 
Yellow, 
Indigo, 
gr. yell, red, blue, gr. 
indigo of 3d order 
22.1 
red, green. 
But the last column here only denotes the thickness of a plate of air which 
would reflect the colours displayed by E« To reduce thenpe the thickness of mica 
