INTENSITY DELATIONS IN THE ST'ECTETEM OF IIEIJUM. 
Table TX. Helinni—Com])arisoii of Series. 
Series. 
A. 
Photo¬ 
graph 
I. 
Photo¬ 
graph 
11 . 
Photo¬ 
graph 
ffll. 
P'hoto- 
graph 
"IV. 
Photo¬ 
graph 
V. 
Photo¬ 
graph 
'■ VI. 
Photo¬ 
graph 
Wll. 
Photo¬ 
graph 
YU I. 
Diffuse .... 
5876 
10 
10 
10 
10 
10 
10 
10 
10 
Sharp .... 
4713 
2-3 
2-7 
2 • 2 
1-4 
1 • 1 
1-1 
absent 
absent 
Principal . . . 
3888 
12-2 
10-2 
7-9 
4 • 9 
4 • 65 
3-8 
4-3 
a1)sent 
Principal Sharp . 
5 • 3 
3-8 
3-6 
3 ’ 5 
3-3 
3-4 
rapidly as the distance increases, lint afterwards more slowly. The true intensity of 
the line X5876 on VII., YIIT. is so small that X4713 could not appear on these 
photographs unless this law were suddenly changed in this region, so that its absence 
presents no difficulty. The Principal series, on the other hand, is not relatively 
intensified at the end of tlie dark space, but is already decreasing in intensity. There 
is evidence of an ultimate reversal at some distance from the cathode (on VII.) but 
it is not conclusive. 
The intensity-ratio of Principal and Sharp series exhibited in the last row of the 
table, clearly shows that the Sharp series tends to become stronger relatively to the 
Principal series, rapidly at the end of the dark space, and afterwards very slowly. 
These phenomena are very definite. 
It is perhaps desirable again to point out that the actual numbers in a table of this 
kind are in no way a representation of the energy emission in the various wave-lengths, 
owing to the curve of sensibility of tire photographic plate. Only the change from 
one column to another has any significance in the present enquirjL 
In the discussion of Parhelium from the same point of view, we may confine 
attention to the lines XX6678, 5047, 5015, belonging respectively to the Diffuse, Sharp 
and Principal series. The intensity of X6G78 is in each case reduced to 10. 
Table X. — Parhelium. Comparison of Series. 
Series. 
A. 
Photo¬ 
graph 
I. 
Photo¬ 
graph 
II. 
I’hoto- 
graph 
III. 
Photo¬ 
graph 
IV. 
Photo- 
gi'aph 
V. 
Photo¬ 
graph 
VI. 
Photo¬ 
graph 
VII. 
Photo¬ 
graph 
VIII. 
Diffuse .... 
6678 
10 
10 
10 
10 
10 
10 
10 
10 
Sharp .... 
.5047 
absent 
0-96 
0-76 
absent 
— 
— 
— - 
— 
Principal . 
.5015 
21-8 
18-9 
15-9 
11-1 
9-0 
10-5 
10-6 
alisent 
We may consider, in the first place, the cases of alisent lines. I he true intensity 
of X6678 on I. is 6’25, and the absence of X5047 from this photograph merely indicates 
VOL. ccxx.—A. 
z 
