Nov. 17, 1881 | 
NATURE 
69 
_ increase in the horizontal force at St. Petersburg, Vienna, Kew, , observations made every five minutes on certain days previously 
_ fixed upon would probably never have shown the way in which 
and Lisbon. At Melbourne in Australia there is a similar dis- 
turbance at the same time both in the declination and in the 
horizontal force. 
Again, between 2 and 3 and between 4 and 5 p.m. there 
fare very small disturbances showing themselves at the same 
absolute time in the horizontal force and declination curves. 
About 5.20 p.m. there is a well-marked increase in the horizontal 
force and eastward deflection of the declination needles. 
About 9.30 p.m. G.T. a storm begins which lasts for about an 
hour. Itis felt inthe northern and in the southern hemispheres, 
near to and on both sides of the equator. At all European 
stations ‘the horizontal force is increased during the first part of 
the storm, and then diminished. 
At Lisbon the vertical force is first increased and then dimin- 
ished, and at St. Petersburg and Stonyhurst there is a diminution 
in the vertical force at the same time as at Lisbon, If we regard 
the declination needles, we find that at St. Petersburg, Zi-ka-Wei, 
and Melbourne, and at Bombay, the declination westward is 
first increased and then diminished, whereas at Kew and Lisbon 
the motions are in the opposite direction. 
The declination at Vienna seems to be intermediate between 
Kew and St. Petersburg, but the curve is incomplete. 
At Bombay and the Mauritius, near to but on opposite sides 
of the equator, the declination needles are deflected opposite 
ways. The local time at these places was from I to 2 o’clock at 
night. 
Now in what way can we account for such magnetic disturb- 
ances as this? If we assume thit by magnetic induction from 
some cause or other the earth’s magnetism is altered, then the 
position of the magnet which would produce the disturbance 
must be such that its pole which attracts the marked end of our 
needle must lie at the beginning of the disturbance tothe east of 
Kew and Lisbon, to the north of Vienna, and to the north-west 
of St, Petersburg ; the Lisbon vertical force curve also shows it 
to be below the surface of the earth. Hence an inductive action 
equivalent to a change of position of the north magnetic pole 
towards the geographical pole would account for these changes. 
The strengthening and weakening of a magnet with its north 
pole to the north on the meridian of Vienna might possibly 
account for the magnetic changes observed between 9.30 and 
10.30 at night, Greenwich time, on March 15, 1879. 
If we attempt to explain this disturbance by currents of 
electricity or discharges of statical electricity in the air above 
the needles, then we must imagine that at first there is a strong 
current from the south-west over St. Petersburg, from the west 
over Vienna, and from the north-west over Kew and Lisbon, the 
vertical force needle at Lisbon showing that the current from 
the north-west lies somewhat to the east of Lisbon, that at the 
Mauritius this current is from the north, and at Bombay from 
the south. > 
Hence we must imagine that a current of electricity passes 
down from north-west to the south-east, going on towards the 
east over Vienna, and towards the north-east over St. Petersburg. 
This must be kept up very much along the same line throughout 
the first part of the disturbance, and then the current or currents 
must be altered in strength in the same manner at all stations. 
We will next consider what would hardly be called a mag- 
netic storm, but a few very small deviations of the magnetic 
needle, lasting from about 5.30 to 7.30 p.m. on March 26, 1879. 
Only the comparison of the originals will give the closeness of 
the similarity of the curves, and the curves for Vienna and Kew 
are absolutely coincident. 
When ‘the declination needle is deflected to the west, the 
horizontal force needle is deflected with its marked end towards 
the south, so that in this disturbance the two needles are drawn 
towards the south-west at the same time with greater or less 
power, and twelve similar bends are clearly traced out in the Vienna 
and Kew curves during the two hours. These disturbances are 
allso very small, that but for the comparison of photographs they 
would probably be lost sight of ; yet we see that the same de- 
flections occur at the same instant at Kew and at Vienna, at St. 
Petersburg and at Melbourne, From the remarkable similarity 
in these disturbances and their occurrence at the same time, we 
should expect that the cause of disturbance is so far removed 
from the places of observation that the difference of their dis- 
tances from it need not be considered. This might not un- 
reasonably be urged as an argument in support of a theory that 
such disturbances are due directly to the action of the sun ‘re- 
garded as ‘a magnetic body. The numerical comparisons of 
these minute changes of magnetic power of the earth at widely 
distant places are related to one another. 
In one or two cases Sefor Capello and Prof, Balfour Stewart 
_ had compared the Lisbon and Kew curves for a particular dis- 
' opportunity of comparing them, 
turbance, but the photographic magnetic records have never 
before been collected from other stations, and there has been no 
From the precise similarity of 
the forms of the curves in many cases we may say that the rate 
of change of magnetic disturbances at widely distant stations is 
thesame, There is nothing fitful or flashing in such disturbances as 
these of March 26, We might imagine a current in the crust of the 
earth ora current or transfer of electricity in the air near to, z.¢. 
within twenty or thirty miles of each of these observatories, but 
to imagine the same current and the same variations of the cur- 
rent at so many different stations, all changing in the same way 
at the same instant, is difficult, unless it can be shown in what 
way all these changes are connected with the cause of such a 
regular electric discharge. It seems easier to imagine that such 
changes as these are due to a change produced by induction in 
the magnetism of the earth itself by some distant body. It is 
easy to show that the magnetism produced by a current in a 
magnetic substance round which it flows is greater in its action 
on a small magnetic needle than the direct action of the current 
itself. Hence a current flowing in the crust of the earth should 
produce its principal effect on a magnetic needle by the mag- 
netic induction which the current induces in the earth itself, 
Sometimes disturbances occur where at the same instant there 
are similar deflections of the declination needles at stations wide 
apart, and suddenly at one of the stations the needle no longer 
goes with the others, but begins to go, and continues: for a con- 
siderable period to go, in the opposite direction to the others, 
turning when they turn, and tracing out a similar curve, but 
turned always in the opposite direction, Such cases occurred 
frequently during March, 1879, and especially on March 23, 
about 1.30 and about ‘7 p.m., Kew time, and on March 29, 
about 9 p.m. An examination of the principal disturbances 
seems to show that : 
(1) A diminution in the horizontal force is accompanied. by 
greater easterly deflections of the declination needle at St. 
Petersburg than at Kew. 
(2) Increase of the horizontal force is accompanied by greater 
westerly deflections at St. Petersburg than at Kew, or is some- 
times accompanied by a westerly deflection at St. Petersburg and 
an easterly deflection at Kew. 
These cases which I have taken will be sufficient to show how 
important it is that there should be additional magnetic observa- 
tories, especially in the southern hemisphere, where photographic 
records should be taken, so that we may learn something about 
the magnetism of the earth. Practically we have to rely on one 
excellent observatory (Melbourne) for the whole of the southern 
hemisphere. Surely the time has arrived when there should be 
photographic registration of the magnetic elements at such an 
important observatory as the Cape of Good Hope, especially 
when the French Government has decided within the last few 
weeks to establish a magnetic observatory at Cape Horn. With 
observatories at Melbourne, at Cape Horn, and at the Cape of 
Good Hope, the southern hemisphere would be well supplied, 
and probably the Russian Government would then soon establish 
an observatory in the east of Siberia. ; 
Now we can readily show the way in which the magnetic 
instruments are disturbed in a magnetic observatory by the 
alteration of the strength of a magnet. Taking magnetic needles 
to represent the declination needle, the inclination needle, and the 
bifilar or horizontal force needle, we may place an electro-magnet 
in a given position with regard to them, and by altering the 
strength of that electro-magnet may cause these needles to trace 
out disturbances of a very decided character. In the disturb- 
ance of March 26 the greatest motion of the needle was not 
more than about 2’ of angle at Kew orat Vienna, It would not 
be possible for me to show you the action on so small a scale. 
I have as yet been speaking of only moderate disturbances, but 
now let us come to some of the larger ones, and I have had the 
opportunity, through the kindness of the Kew Committee, and the 
observers at the various observatories mentioned, of studying the 
curves for the August magnetic storm which began at 10.20 a.m. 
-Greenwich time, on August 1Tth, and for convenience may be 
divided into three storms, one lasting from 10.20 on the 11th, to 
Ia,m, on'the r2th; a second from 11.30a.m, on the 12th to 
