68 
PEOFESSOE J. CLEEK ilAXWELL OX 
and (9.) 
Aj — Ag 
Having thus found N and K, we may find the wave-length corresponding to the dark 
band n from the formula 
^ ( 10 .) 
X = 
N + n 
In my experiments the line D corresponded with the seventh dark hand, and F was 
between the 15th and 16th, so that W2=15‘7. Here then for D, 
and for F, 
whence we find 
Xi=2175'i. 
^2=15-7X2=1794/^ 
N=34, R=89175. 
Fkaunhofee’s measure. 
( 11 .) 
( 12 .) 
There were 22 bands visible, corresponding to 22 different positions on the scale AB, 
as determined 4th August, 1859. 
Band. 
Scale. 
Table I. 
Band. Scale. 
Band. 
Scale. 
n— 1 
17 
n— 9 
36 
W= 16 
57 
2 
19 
10 
39 
17 
61 
3 
11 
42 
18 
65 
4 
231 
12 
45 
19 
69 
5 
26 
13 
48 
20 
73 
6 
281 
14 
51 
21 
rr ^ 
i i 
7 
31 
15 
54 
22 
82 
8 
331 
Sixteen equidistant points on the scale were chosen for standard colours in the experi- 
ments to be described. The following Table gives the reading on the scale AB, the 
value of N -{-w, and the calculated wave-length for each of these : — 
Table II. 
Scale. 
(N + m) . 
"Wave-length. 
Colour. 
20 
36-4 
2450 
Bed. 
24 
38-3 
2328 
Scarlet. 
28 
39-8 
2240 
Orange. 
32 
41-4 
2154 
Yellow. 
36 
42-9 
2078 
Yellow-green. 
40 
44-3 
2013 
Green. 
44 
45-7 
1951 
Green. 
48 
47-0 
1879 
Bluish green. 
52 
48-3 
1846 
Blue-green. 
56 
49-6 
1797 
Greenish blue. 
60 
50-8 
1755 
Blue. 
