208 
PROFESSORS G. D. LIVEING AND J. DEWAR ON 
Magnesium Lines. 
I. 
II. 
III. 
IV. 
V. 
VI. 
VII. 
VIII. . 
IX. 
hundredths 
wave- 
O 
/ 
u 
of an inch. 
o 
t 
Q 
/ 
n 
o 
/ 
n 
length. 
129 
301 
4 
55 
67 
68-67 
-1 
10 
45 
299 
54 
10 
128 
301 
4 
55 
67 
68-85 
-1 
10 
58 
299 
53 
57 
131 
300 
54 
55 
67 
59-32 
-1 
1 
7 
299 
53 
48 
299 
54 
4 
134 
300 
4 
55 
75 
10-67 
-0 
10 
53 
299 
54 
2 
135 
300 
4 
55 
75 
1039 
-0 
10 
36 
299 
54 
19 
139 
300 
0 
3 
72 
5-66 
-0 
5 
47 
299 
54 
16 
140 
300 
0 
3 
72 
5-95 
-0 
6 
6 
299 
53 
57 
137 
38 
10 
0 
75 
8 75 
+ 0 
8 
56 
38 
18 
56 
138 
38 
15 
0 
72 
342 
+ 0 
3 
30 
38 
18 
30 
125 
37 
20 
5 
67 
56 82 
+ c 
58 
32 
38 
18 
37 
124 
37 
30 
5 
70 
47-33 
+ 0 
48 
35 
38 
18 
40 
38 
18 
41 
49 
12 
19 
2779-4 
137 
38 
10 
0 
75 
30-88 
+ 0 
31 
31 
38 
41 
31 
138 
38 
15 
0 
72 
25-68 
+ 0 
26 
18 
38 
41 
18 
38 
41 
25 
139 
300 
0 
3 
72 
27-86 
-0 
28 
32 
299 
31 
31 
140 
300 
0 
3 
72 
28-02 
-0 
28 
42 
299 
31 
21 
299 
31 
26 
49 
35 
0 
2795 2 
306 
299 
15 
0 
86 
8-75 
+ 0 
8 
49 
299 
23 
49 
299 
23 
50 
307 
38 
45 
0 
86 
10-89 
-0 
11 
1 
38 
33 
59 
308 
38 
30 
0 
85 
3-84 
+ 0 
3 
52 
38 
33 
52 
38 
33 
55 
309 
299 
30 
0 
85 
6-10 
-0 
6 
9 
299 
23 
51 
49 
35 
2 
2795-2 
137 
38 
10 
0 
75 
41-09 
+ 0 
41 
56 
38 
51 
56 
138 
38 
15 
0 
72 
35-83 
+ 0 
36 
42 
38 
51 
42 
38 
51 
49 
139 
300 
0 
3 
72 
37-82 
-0 
38 
44 
299 
21 
19 
140 
300 
0 
3 
72 
38-21 
-0 
39 
8 
299 
20 
55 
299 
21 
7 
49 
45 
21 
2802-4 
306 
299 
15 
0 
86 
1-57 
-0 
1 
35 
299 
13 
25 
307 
38 
45 
0 
86 
059 
-0 
0 
36 
38 
44 
24 
308 
38 
30 
0 
85 
14-16 
+ 0 
14 
17 
38 
44 
17 
38 
44 
21 
309 
299 
30 
0 
85 
16-48 
-0 
16 
37 
299 
13 
23 
299 
13 
24 
49 
45 
28 
(2802-4) 
303 
40 
0 
0 
85 
2-97 
-0 
3 
0 
39 
57 
0 
304 
298 
0 
0 
85 
0 34 
+ 0 
0 
21 
298 
0 
21 
305 
298 
5 
0 
85 
4-48 
-0 
4 
31 
298 
0 
29 
298 
0 
25 
50 
58 
18 
2852-C 
Remarks on the foregoing tables. 
It will be observed that when two or more independent determinations have been 
made the wave-lengths found are often identical, rarely differ by more than '2 of a 
tenth-metre. This seems to make the probable error in most cases very small—smaller 
than we venture to think it really may be, for there are one or two sources of error 
which are quite sufficient to account for a variation of '2 of a tenth-metre in the wave¬ 
length. First the sliding tubes of the telescope, for it has a draw tube as well as the 
usual rack and pinion arrangement for focussing, in order to allow for the great varia¬ 
tions in the focal distance of the uncorrected quartz lenses, and such sliding tubes 
have always some play, so that in the operation of reversing the photographic plate 
by turning the sliding tube about its axis there might easily be a small displacement. 
