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

DECLINATION NEEDLE.

Every change in this instrument from one position to
another was by sudden impulses ; after each of these it
was stationary, for intervals varying from 5 sec. to 20 sec. ;
then it was forced again to another position, and was
again stationary without the slightest motion ; and so on
successively. _

At 3h. 30m. the changes from one position to another
became very decided, but the motions still partook of
the same character ; absolute rest and jerking motion
followed alternately. In 2 sec. or 3 sec. the neele fre-
quently moved through many minutes of arc, and then
suddenly became stationary again.
At 3h. 36m. 20sec. Pail, a bold sweep carried the north
end of the needle towards the west 56m. of arc, in one
minute of time ; at 3h. 37m. 20 sec. the theodolite read
245 d. 22m. ; and for two minutes after this time the
cross carried by the needle was out of range of the te-
lescope,* being in a position, in which, if the telescope
had been exactly directed to it, the theodolite would have
read. less than 245 d. 22m. At 3h. 40m. 20 sec., P.M.,
Gottingen mean time, the needle had moved back 25w.;
at 3h. 43m. 50 sec. the theodolite read 246 d. 19m. ; at
3h. 44m. 20 sec. the needle had moved so far (north end
towards the east) that the theodolite reading was 247 d.
38m., and the cross carried by the needle was out of
range of the telescope on the opposite side.
This extraordinary magnetic stride, of more than 21
deg., was traversed in about Bm., the extremes being only
separated by that interval of time.

At both extremities the needle was without swing, all
momentum from such a. wide sweep being huite destroyed.
After remaining at this place for more than two
minutes, the needle slowly returned, and at 3h. 48m. 54 sec.
the theodolite read 246 deg. 27 min.; at 3h. .53m. 21 sec.
it read 246 deg. 37m. Within 5 sec. after this, another
bold sweep carried the cross out of the range of the
telescope ; when found at 3h. 54m. 40 sec. the theodo-
lite read 245 deg. 31 min. ; instantaneously it rushed
back, with a violently agitated motion across 'and out of
the field on the other side; the circle reading at 3h. 55m.
was 246 deg. 43 min., and therefore this arc of 1 deg.
12 min., was passed over in 20 secs. of time.
This was the last very great excursion ; the needle
was incessantly watched for nine hours longer, during
which time it was much agitated. The most remarkable
changes are the following:—

H. M. S. D.M.
At 4 25 36 P.M. Gottingen m. t., theodolite read 246 8
31 36 34
49 36
4 55 36
5 46 37
50 37
6 0 30
6 33 37
6 46 36
7 16 38
7 31 38
7 56 38
8 53 38
9 18 38
9 38 38
10 10 39
10 41 39
10 46 39
11 45 40
12 52 40

30
... 8
.2362
...
... 25
... 46

28
...
43 ...

53
39
46
30

It is to be remembered that increasing readings denote
that the North end of the needle moves towards the East.

VERTICAL FORCE MAGNETOMETER.

The vertical force magnetometer was as much affected
as the declination instrument. The disturbances of its
vibrations were very . similar, except that it was fre-
quently much longer in the stationary state, its times of
rest varying from 5 sec. to 2m. ; at the end of each of
these it jumped on, then was again still, and so on.
This instrument had been much affected early in the
morning ; the extent of its excursions being between
37d.9, and 44d.1 on the scale. The following are scale
readings, commencing with noon :
H. M. S. D. M.
At 0 0 0 (n.) Gottingen mean time, scale reading 44 0
1 47 30 P.M. ... ... 47 8
1 57 30 ... ... 48 1
2 7 30 50 0
••• ..•
3 15 21 55 0 '
••• •••
3 16 21 ••• ••• 559
3 21 26 ... ••• 579
3 22 21 ... ••• 58 3
3 22 51 ... ••• ' 590
3 23 21 ••• ... 603
3 23 51 ••• ••• 603
3 24 21 •••
—• 604
3 26 21 ••• ••• 63 0
3 27 51 •••
••• 632
3 31 21 ••• ••• 67 0
3 32 21 •••
• ••• 69 5
3 32 51 •••
3 34 21 ••• ••• 71 2
e needle (which is
3 34 51 •••
t2hle, theeas endt,mtahreke.••• 81 3
or the 0
needle being transverse tcl9sthe
magnetic meridian),
towa3rd3ss
was resting
apparatus intended for guarding theon
the eastern Y, or
much as the frame permitted it, and heldneedle, dipping as
by a great power ;in this • • there apparently
minutes, till 3h. 4:5m,
situation it remained for ten
H.M.S.
At 3 45 42 p.m.Gott. D. M.
346 23 Gottingen mean time,scale read 73 1
3 50 31 ••• ••• 68 9
. 357 38 ••• • • 6834 4
... % ... 57
3 58 58
••• 55 6
...
4 13 36
••• 62 9
4 29 26 ...
••• ... 669
5 21 37 ... ... 55 6
5 44 37 60 6
... ...
5 55 37 52 2
... ...
6 19 7 68 3
... ...
717 8 53 8
... • •
7 35 8 ... ... 503'
922 9 ... ... 4561
Sept. 25.11 039 40 9
... ...
Sept. 26. 058 25A.m. ... 33 7
1 325 ... ... 36 1
About 6h. 19m. r.m. the needle assumed a steadier ap-
pearance, having a motion som?thing like vibration, but
exceeding irregular.
HORIZONTAL FORCE. MAGNI:TONI:TER.
The horizontal force magnetometer was not less
affected than the other two instruments. The ef-
fect on its vibrations was, however, peculiar to it-
self ; in the midst of its swings it was suddenly
checked, and held in that place for a second or
two, then hurried backwards, again suddenly stopped, and
then forced back in the contrary direction ; these cheeks
were sometimes at 5 sec.. sometimes at 10 sec., after ar-
riving at its limit. They were most striking. From ex-
perience with this instrument, we are accustomed to look
for an almost imperceptible motion at the extvrnities of
the variations, then to see It 11101,0 slowly in the opposite

//~~

EVENING Sex.

- _
direction, (pickily in the centre of swing, slowly towsads
the end, then retts'rn, and so on ; tto see it, almost in
the same instant, moving rapidly, an absolutely motion-
less, was very striking and strange itbe observeri.
This instrument was less affected die early part of
the day than either of the others. About noon it showed
signs of being under the influence of some disturbing
cause : the scale then read .55d. R ; at lh. 50m. the read-
ing increased to 58d. 6 ; at 211. Om. to 59d. 3 ; at 2b.
15m. to 60d. 1 ; it then oscillated between 59d. and 61d..
till 3b. 11m., the scale then reading 59d. 7. The dis
turbances now became as surprising as those with o.le
other needles ; a steady and rapid increase of scale
reading took place, with a strange jerking motion.
H. M. S. Dr JL,
At 3 14 48 P.M., Gottingen mean time, the scale read 61 4
3 21 3 ••• ••• 61 2
3 27 26 64 2
3 28 6 ••• ••• 64 4
3 28 46• 64 8
333 16
••• 73 6
3 38 56
••• 73 2
Then there was a remarkable start to 78d. 0 ; and,
here it remained stationary from 3h. 39m. to 3h. 43m.,
when it started back.

Et N. S.
D. 111.
At 3 47 41 P.u., Gottingen mean time, the scale read 69 9
3 56 31 ...
... 65 6
4 0 51 ... ... 63 7
4 8 55 .• • ... 63 1
4 15 1.1 ... ... 64 6
• 4 47 41 ..-. ... 61 4
Then the reading increased a little, and then g-raduallv
decreased, till sh. 53m. 12sec. P.M., Gottingen mean time,
when it read 57d. 8; it then increased to 6h. 16m. I.4ice.,
when the scale read 62d. 1.

It then oscillated between 58d. and 60d., until 7h. 25m.
13sec., when a sharp diminution to 53d. 9 took place.
The readings alternately increased and decreased for the
next 6 hours, oscillating all the time between 33d. ands7d.
From the preceding account it will be seen that the
magnetometers were more affected on this day than ever
before, and that the great disturbance affected the three
instruments at the same time.

The most abrupt and violent fluctuations of the meri-
dian needle occurred between 2h. 36m. and 3h. 46m. At
3h. 35m. 21sec. the vertical force magnet went beyond
the scale: at 3h. 45m. it again came on. The horizontal
force needle began its great deflection before 3h. 38m.
16sec. ; it was over at 3h. 38m.; and probably, had there
been an oLserver at each instrument, it would have been
found that the effects on all were simultaneous. Such
was Mr. Glaisher's impression while observing; but (as
he remarks) the startling and -bewildering effect of so
great changes was such, that all that he could do was to
make such observations as seemed practicable, with a
view of discovering the extent of such extraordinary dis-
turbances.

After this great disturbance the irregularities were
still very great ; the horizontal force and the vertical
force magnetometers partook of similar disturbances
throughout. With a few trifling exceptions, an increase
of force 'in one was accompanied with an increase of
force in .the other, and so also with respect to the de-
crease of ft:wee.

The declination magnet has certainly, however, one
great deflection, in which the others have no share ; that
which occurred bet ween 3h. 54m. 40sec. and 3h. 55m. Osec.,
where an arc of 1 deg. 12m. was described in 20sec.
Nothing similar, at this time, is shown by either of the
other needles.

In addition to the observations contained in this ac-
count, ample and abundant observations were taken to
obtain every variation of the vertical force, and also
observations of the declination and horizontal force mag-
netometer sufficient to show every great change, and
nearly all the small ones, until Sept. 26, lh. A.m., when
the observations were discontinued.

At 4h. 40w. an observation of the dip wat taken, giving
a result greater than ordinary.
The day. (Sept. 25) was cloudy throughout : about
9h. P.M , a few bright streamers were seen through the
clouds, then nothing more till 1111. P.M., when an au-
roral arch, about 24 deg. high, was visible for a short time.
It is desirable that accounts of corresponding obser-
vations of this disturbance should be collected. I invite
observers who may have made observations on the same
day to send to me abstracts of their observations, or to
communicate them, in the way which they think best, to
the public, or to the persons who are interested in mag-
netical phenomena. G. B. AIRY.

This arose from the great inclination of the axis of the
collimator (carried by the magnet) to the magnetic meridian;
in consequence of which the pencil of rays passing through
the object-glass of the collimator was thrown entirely on one
aide of the object-glass of the theodolite. In ordinary cases,
the change of angle has been sufficiently slow to allow the ob-
server to shift the suspension of the magnet, hut the rapid
changes on Sept. 25 did not allow the observer to leave his
place. Observations with the mirror in Gauss's manner are
free from this inconvenience.

/r