430 ON THE OEEAT MAONETIC DISTTJEBANCE OF AEG. 28 TO SEPT. 7, 1859. 
and this discharge will be in one direction for an increase, and in the opposite direction 
for a diminution of the primary current. 
Disturbances would thus seem to be due to the absolute amount of the primary 
current, and auroras and earth-currents to the rapidity with which this current changes. 
Let me remark, in conclusion, that if it be true that the spots on the surface of our 
luminary (or action connected with these spots) are the primary cause of magnetic disturb- 
ances, it is to be hoped, since the study of the sun’s disc is at present a favourite subject 
with observers, that ere long something more definite may be known with regard to the 
exact relation that subsists between these two great phenomena. 
Explanation op the Plates. 
Plate IX. contains reduced tracings of the declination curves. 
Plates X. and XI. those of the horizontal and vertical force curves. 
The curves run in order of time from the top to the bottom of the Plate, also from 
left to right. 
The precise Kew mean time of the commencement and end of each curve is as fol- 
lows : — 
d 
h 
m 
d 
h 
m 
No. I. Aug. 
II. 
27 
28 
22 
23 
21i 
27 
to Aug. 28 
29 
22 
22 
Qi 
d 
[■declination Aug. 29 
li m 
0 27 to 
III. 
29 
22 
13 
77 
55 
30 
22 
10 
L Aug. 29 
22 91 
IV. 
30 
22 
20i 
55 
31 
22 
9A 
V. Sept. 
0 
22 
m 
55 
1 
22 
Qi 
^2 
VI. 
1 
22 
19i 
55 
2 
22 
y 2 
VII. 
2 
22 
18 
55 
3 
22 
91 
y 2 
VIII. 
3 
22 
12 
55 
4 
22 
11 
IX. 
5 
0 
17 
55 
5 
22 
1 
X. 
5 
22 
21 
55 
6 
22 
14 
XI. 
6 
22 
25 
55 
7 
22 
9 
XII. 
7 
22 
12 
5^ 
8 
22 
9 
