152 Disturbance of the Earth’s Magnetism. 
usual at 10 o’clock; that it increased until 10h. 374m. when it was 
greater than in its undisturbed state ; and that it again decreased, and 
was less than usual the next morning at 7h. 20m. 
By adding five hours to the time of the observations made at Alba- 
ny, we shall have nearly the corresponding time at Mr. Christie’s res- 
idence in Woolwich. 'These times being 6h. and 10h. P. m. will 
therefore correspond with 11h. Pp. m. and 3h. a. m. of time at Wool- 
wich. From this it appears, that the observations at Albany were 
made at a period of absolute time between the last observation of 
Mr. Christie on the evening of the 19th, and the morning of the 20th. 
The only interesting result, however, which apparently can be drawn 
from a comparison of the observations, is, that at both places there 
was a disturbance of terrestrial intensity at the same time; the inten- 
sity rising above and sinking below its usual state at each, although 
these changes did not occur in the same order at both places. 
I am not aware that a simultaneous disturbance of terrestial mag- 
netism, in connexion with an aurora, has ever before been noted at 
two places so distant from each other. Nor do I think the coinci- 
dence in this case in the least degree accidental. On the contrary, 
it appears to me highly probable that the disturbing cause was not 
only common to both places, but was also active at the same time 
in a great portion of the northern part of the globe. A brilliant au- 
rora is by no means a local phenomenon. ‘That of the 28th of Au- 
gust, 1827, was visible over nearly the whole of the northern States, 
in Canada, and also from some part of the Atlantic ocean. But 
what places the extensive and simultaneous appearance of the auro- 
ra in a more striking point of view than any in which it perhaps was 
ever before exhibited, is the comparison of the notices of the aurora 
given under the monthly meteorological reports in the Annals of 
Philosophy for 1830 and 1831, and the Reports of the Regents of 
the University of the state of New York for the same period. By 
inspecting these two publications, it will be seen, that from April 
1830, to April 1831 inclusive, the aurora borealis was remarkably 
frequent and brilliant, both in Europe and in this country; and 
that most of the auroras described in the Annals for this time, partic- 
ularly the brilliant ones, were seen on the same evening in England 
and in the State of New York. 
The particular days on which the aurora appeared in England, 
are not mentioned in the Annals, except when the aurora, is con- 
sidered on some accounts interesting. By comparing those which 
