OF AUGUST 28 TO SEPTEIkIBEE 7, 1859. 
425 
similar manner, tlie separating values (corresponding to 3'‘3 for the declination) being 
for the horizontal force ’0014 of its whole amount, and for the vertical force •000478 
of the whole. 
I now proceed to notice some of the peculiarities of this magnetic storm. 
It appears that we have two distinct well-marked disturbances, each commencing 
abruptly and ending gradually, the first of which began on the evening of August 28, 
and the second on the early morning of September 2. These two great disturbances 
correspond therefore in point of time to the two great auroral displays already alluded to. 
The average effect of the disturbance of August 28 was to increase the declination, 
and to diminish the horizontal and vertical components of the earth’s magnetic force. 
The appearance of the curves indicates very well the modus operandi of the disturbing 
force on this occasion. From their serrated appearance, it will be seen that a force 
tending to increase one of the elements was generally followed after a short interval by 
one of the opposite description, and vice versa. The exertion of the disturbing force 
was thus of a throbbing or pulsatory character. The interval of time between two of 
these minute pulsations may be said to have varied from half a minute, or the smallest 
observable portion of time, up to four or five minutes. 
This pulsator}' character of the disturbing force agrees well with the nature of its 
action on telegraphic wires, in which observers have noticed that the polarity of the 
current changes very frequently. 
Apart from these comparatively rapid and minute changes, the curves referring to this 
great disturbance indicate, for all the elements, pulsations in the disturbing force which 
have a period of from forty to fifty minutes. These pulsations are of a very violent 
character in the case of the declination, where the ebb and fiow of the force alternately 
carries the needle above and below its normal position. 
We have thus, as it were, two sets of waves, the first or smaller of which is superim- 
posed upon the second or larger, just as in the ocean we sometimes see ripples caused 
by the wind traversing the surface of a great wave. But in addition to these there is a 
still more remarkable period which this great disturbance seems to have accomplished 
for all the elements in about six hours from its commencement, after which it started 
anew in the same direction as at first, to accomplish another period or grand wave, which 
lasted about the same time. The violence of the disturbance seems to have exhausted 
itself in the accomplishment of these two grand waves ; for after this, although the 
needle was far from tranquil, yet its evagations were of a more moderate description. 
Three periods are thus observable, — 
1. That extending from half a minute up to four or five minutes. 
2. A period of from forty to fifty minutes. 
3. A period of about six hours. 
It is impossible to state with accuracy what were the greatest departures from the 
mean values caused by this disturbance, as the curves for all the elements went beyond 
the sensitive paper ; very approximately, however^ we may estimate these as follows : — 
3n2 
