INTENSITY RELATIONS IN THE SPECTRUM OF HLLIU.M. 
145 
The experimental measures of the lieights of the various lines in each case are given 
in the following table, together with the density gradients of the wedge per millimetre 
at each wave-length, determined from the graph of density gradient in the manner 
already described. The table contains all tbe experimental data from which the 
ensuing conclusions are drawn. As these conclusions are of a very general nature, it 
was thought necessary to give the measurements relating to one set of photographs 
in complete detail. 
The photographs are described by Roman numerals. 
Table I. 
A. 
4. 
Photo¬ 
graph 
I. at 
cathode. 
Photo¬ 
graph 
II. at 
1 mm. 
Photo¬ 
graph 
III. at 
2 mm. 
Photo¬ 
graph 
IV. at 
3 mm. 
Photo¬ 
graph 
V. at 
4 mm. 
Photo¬ 
graph 
VI. at 
5 mm. 
Photo¬ 
graph 
VII. at 
6 mm. 
Photo¬ 
graph 
VIII. at 
7 mm. 
h. 
h. 
h. 
h. 
h. 
h. 
h. 
h. 
6678 
0 • 329 
7-7 
12-7 
12-3 
10-8 
7-4 
5 - 2 
2-9 
5876 
0-396 
9-4 
13-1 
13-6 
13-2 
11-1 
9-5 
7-9 
3-4 
5047 
0-414 
— 
2-3 
1-2 
— 
__ 
— 
-- 
— 
5015 
0-415 
8-7 
12 - 2 
11-3 
8-9 
6-0 
4-3 
2-5 
— 
4922 
0-415 
4-0 
7-2 
6-9 
5-4 
3-3 
1-7 
— 
— 
4713 
0-420 
4-0 
8-0 
7-8 
6-0 
3 - 9 
1-8 
— - 
— 
4686 
0-421 
0-6 
— 
— 
__ 
— 
— 
4472 
0-453 
10-0 
13-4 
13-2 
12-7 
11-2 
9-8 
8-1 
3-9 
4437 
0-461 
— 
2-0 
— 
— 
— 
— 
— 
4388 
0-475 
3-3 
5-2 
5-3 
4-8 
3-8 
1-9 
1-1 
— 
4144 
0 - 569 
— 
1-8 
1-7 
just seen 
— 
—- 
— 
— 
4121 
0-582 
— 
2-0 
2-0 
just seen 
— 
— 
— 
— 
4026 
0 - 650 
3-2 
5-4 
6-0 
5 - 7 
4-2 
3-0 
1-9 
— 
3965 
0-707 
2-0 
3-3 
3-3 
2-1 
just seen 
— 
— 
— 
3888 
0-815 
4-9 
6-4 
6-2 
5-2 
4-1 
3-0 
2-4 
The magnification of the various photographs was not completely identical in all 
cases. On the original plate, the distance between the lines \\6678, 3888, was 
44"95 mm. If this distance be measured’ on any individual photograph, its 
magnification m is deduced by simple division. On photographs I.-V. inclusive, we 
found m — 3'181, and on photographs VI.-VIII., m = 3‘159. 
Some of the Helium bands appear on the intermediate photographs, though absent 
very close to the cathode, and again at some distance from it. They are, in fact, only 
shown on the photographs IV.-VII., according to the details set forth in Table II. The 
wave-lengths are only rough values serving to identify the individual bands, and the 
values of dx are obtained as before from the calibration curve of the wedge. We 
merely record in the table some of the more conspicuous examples of these bands, as 
an illustration of their behaviour. We do not propose to discuss them, for they are 
in reality band heads consisting of a large number of nearly overlapping lines, and 
VOL. OCXX.-A. 
Y 
