24*8 M. Kreil’s Magnetic Ohsermtions* 
to be taken from those which are ascribed to the first hour 
in the morning when the apparatus was observed. It follows 
that much fewer disturbances begin at that hour than in the 
evening. It is remarkable that a disturbance hardly ever 
begins in the latter hours of the forenoon. 
19. The perturbations appear to commence for the most 
part suddenly, as by shocks. At least it was so in those cases 
in which the phsenomenon began under our eyes, that is to 
say, at the time of an observation. It was so on the 18th of 
February 1837j on which day an aurora showed itself with 
a magnificence unusual in this country. Two series of transits 
of a division of the scale across the wire had been observed 
as usual. In the first series at 38"^ these passages agreed 
to a tenth of a second of time; — a proof that the needle was 
still performing its minute vibrations with perfect regularity ; 
nor in the preceding observations of the same day was any 
trace of disturbance to be discovered. In the second series, 
which was made 12 minutes later, there w^ere differences of 
2 seconds of time, and the needle was visibly drawn back- 
wards and forwards by the disturbing forces. I may be per- 
mitted to mention one more among many similar cases. It 
is that of the very great disturbance of the 14th of November 
1837, at which time we were making magnetic observations 
for three days uninterruptedly from 5 to 5 minutes, and when 
necessary at still shorter intervals, for the purpose of exami- 
ning whether the periodical phsenomenon of the falling stars 
was or was not connected with magnetism. Between 10 and 
1 1 in the evening the needle appeared pretty tranquil, al- 
though earlier in the day it had been much disturbed. The 
observer, Sig. Della Vedova, was engaged in observing the 
passage of a division of the scale across the wires, and had 
chosen for that purpose a division nearly in the middle of the 
arc of vibration, which was then about 7^ when all at once, 
at ID 7', he saw that this division did not come to the wire, 
although it had taken its direction towards it ; but before 
reaching it, the needle had turned the opposite way, and im- 
mediately after the scale disappeared from the field of view, 
which was left quite dark. The observer, thinking that the 
lamp which illuminates the scale had gone out, was about to 
rise in order to light it again, when he saw the scale suddenly 
reappear, move rapidly across the field, and disappear on the 
opposite side. The rapidity of the movement indicated a 
much larger arc of vibration. The arc had in fact increased 
40 minutes without any apparent cause. As the observations 
could not be exact whilst the vibrations were so great, Sig. D. 
Vedova was about to employ a magnetic bar which is always 
