146 Disturbance of the Earth’s Magnetism. 
In April, 1831, a new series was commenced, to determine if the 
needles still indicated the same degree of magnetic intensity. 
material difference was observed, except in the following instance, 
when a remarkable anomaly was exhibited. é 
On the 19th of April, at 12 o’clock at noon, an observation was 
made with the Hansteen needle, the result of which differed only 
the fractional part of a second from the usual mean rate of this 
e. At6 o’clock Pp. m. the same day, another observation was. 
made with the same needle, and apparently under the same circum- 
stances; but a remarkable change was now observed in the time of 
its making three hundred vibrations, indicating a great increase in the 
magnetic intensity of the earth. It was at first supposed that the 
fixed for the purpose, in the Academy Park, at a sufficient distance 
from every disturbing object, and with the usual precaution of di- 
vesting the person of all articles of iron, such as keys, knives, &c. 
t about 9 o’clock in the evening, or three hours after the above 
observation, an unusual appearance was noticed in the southern 
part of the heavens, which was shortly afterwards recognized as an 
arch of the aurora. It was about nine degrees in breadth, with the 
vertex of the arch twenty degrees above the horizon. At this time 
the northern part of the sky was covered with light fleecy clouds. 
At forty five minutes past nine, the clouds partially disappeared, and 
disclosed the whole northern hemisphere entirely occupied with co- 
ruscations of the aurora, shooting up past the zenith, and apparent- 
ly all converging to the same point. The actual formation of a co- 
The result of the observation was, however, entirely different 
an uncommonly degree of magnetic intensity, it howed an 
intensity considerable lower ee =e 
* 
