The Sun.
London, England, 1841-11-25 00:00:00

PRICE 5d

RGYAL OBSERVATORY, GREEN-

WIC H.
EXTRAORDINARY DISTURBANCE OF THE

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MAGNETIC ---&STRITMENTS.
(From the Cambridge Advertiser.)
Royal Observatory,-Greenwich, Oct. 26.
On the 25th of September of the present year, a most
extraordinary disturbance of the magnetic instruments
was observed at the Magnetic Observatory attached to
the Royal Observatory of Greenwich. The disturbed
state of all the instruments attracted the attention of Mr.
Glaisher (chief assistant in the Magnetic Department),
at an early hour of that day, and he immediately com-
menced a series of observations on all the instruments
at short intervals. After a time the disturbance became
so small that the extraordinary observations were dis-
continued ; but it again increased, and observations were
again immediately made with all the instruments, and
repeated as rapidly as it was possible for one observer to
do so. But for the promptitude and judgment displayed
by Mr. Glaisher on this occasion, the record of this dis-
turbance, unprecedented in this magnetic latitude, would
probably have been lost. The following statement will
give an idea of the magnitude of the disturbance : that
within eight minutes of time, the declination needle
changed its position more than 2+ deg. (having passed
in both directions the range of the observing telescope,
which includes that angle): that the verticle force was
increased by more than 1-40th of its whole value, the in-
strument having then reached the extremity of its
range; and that the horizontal force was increased about
1-30th of its whole value.

The following more detailed account is taken princi-
pally from the abstract furnished by Mr. Glaisber. It is
to be remarked that the time throughout is Gottingen
mean solar time, civil reckoning ; that the readings of the
theodolite for the declination needle increase as the north
end of the needle moves towards the east, and that the
reading for the astronomical meridian is 269 deg. 51 min.
45 sec. nearly ; that the increasing readings ri thererti-
cal force magnetometer imply increasing vriiicaVoree,
one division being eqaul to 0.00471 of the whole vertical
force ; and that the increasing readings of the horizontal
force magnetometer imply increasing 'horizontal force,
one division being equal to 0.002214 of the whole hori-
zontal force.

Early in the 'morning of the 25th of September, the
needles were in an agitated state. During the appear-
ance of an aurora additional observations were taken,
and the declination needle in less than three hours tra-
versed an arc of 34 min. After this the needles were in
a tolerably quiet state, and extraordinary observations
were discontinued.

The observation at 10h. a,m. showing a charge of 17
min. of arc from the previous reading, at Bh. A.M., extra
observations were again resumed, and continued till 11h.
A.M. ; nothing remarkable appearing during this time,
they were again discontinued.

At 2h. Gottingen mean time, it was evident that
all the needless were affected by some unusual cause of
disturbance, and incessant observations were at once
commenced, the instruments being observed successively
as quickly as one observer could take them. At 3h. 53m.
Mr. Hind joined, and subsequently Messrs. Dunkin and
Paul. From this time to the discontinuance of the ob-
servations two persons were constantly engaged, one
taking the observations with the vertical force magneto-
meter—the other those of the declination needle and of
the horizontal force magnetometer. About 2h. 40m. P.M.
the motions of the needles became very peculiar ; the
vibrations of the declination needle and of the vertical
force magnetometer being quite destroyed ; and those of
the horizontal force magnetometer being reduced to a
continuous succession of jerks or starts. it wilt, perhaps,
contribute to clearness if the motions of the three instru-
ments are now separately described.