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tail ; but the direction of this tail would depend on the motion of the comet,
as well as on the intensity of the force.

It does not necessarily follow because the tail points away from the sun,
that the force which repels it must entirely overcome the effect of the sun's
attraction ; but it can be shown that, even for those comets whose tails show
the most curvature, the force must be comparable with the sun's gravitation ;
and to produce the straight tails which comets sometimes possess, it would
require a force of almost infinite intensity, if it acted as gravity does on
ordinary matter. It has been found by Professor Norton that if the bent
tail of Donati's comet were composed of ordinary matter, leaving the comet
under the action of a repulsive force in the sun, this force must be between
1'5 and '39 of the sun's attraction, the matter in the leading edge being
repelled by the former, and that in the following by the latter.

If the force is electrical, its intensity will depend on the charge of
electricity in the vapour; and if there are several streams of vapour
variously charged, these would each form a tail of distinct curvature ; so
that the comet might have several bent tails, or even a fan which are
features not uncommonly observed. This, then, affords an explanation of



3 A] ON COMETARY PHENOMENA. 21

the great variety of bent tails often seen with comets, and even of those
pointing towards the sun ; for some of the vapour might have a charge of
the opposite electricity to that in the sun, under which circumstance it
would be attracted. But, so far as I can see, the straight tails which are so
often seen, and sometimes in conjunction with the curved ones, can only be
explained in the manner described in my previous paper before this Society
(see Paper No. 2, p. 7) as an electric brush or discharge through space.

As a probable cause of the electricity in the vapour of the comet, I
would suggest that the evaporation taking place from the surface of the
comet, might cause a crust to form there, through which the subsequent
vapour would have to force its way in the form of jets, which, like the jets
from Armstrong's hydro-electrical machine, might issue charged with elec-
tricity, the solid being charged with electricity of the opposite kind. If this
were the case, the vapour, as it formed an atmosphere round the nucleus,
would discharge some of its electricity back, and so cause those portions
of the atmosphere near the solid to be self-luminous ; and, besides this, there
might be other discharges, between the clouds, or outwards into the medium
of space, so as to illuminate a part of or the whole atmosphere.

On this hypothesis, if the vapour of the tail is charged with electricity
of one kind, say negative, the solid head must leave the neighbourhood of
the sun charged with positive electricity, which, as it gets further from the
sun, and evaporation becomes feeble, will at length overpower the negative,
and charge the atmosphere of the comet, which would then be attracted by
the sun instead of repelled ; so that the tail, if it had one, would be towards
the sun ; or else, if by this time the comet had no atmosphere, it would carry
off its charge, and (unless it lost it en voyage) on its next appearance it
would be charged with positive electricity, and the first vapour would probably
be attracted instead of repelled, and the first tail point towards the sun.

Thus a comet, as it left the sun, would arrive at a point where it had no
tail, and afterwards would commence a tail towards the sun. This tail
would not make much show on the comet's departure ; for the evaporation
continues to a much greater distance from the sun on the departure, than
that at which it commenced ; but if the comet returned it would make its
first appearance with a tail towards the sun, which, as the evaporation in-
creased, and the comet enlarged, would soon take the opposite direction.

There seem to have been some instances where comets have been first
seen with a tail towards the sun, which they have afterwards changed ;
indeed this is said to be the case with Encke's comet, now visible ; so that
this is another instance of the remarkable way in which the actual
phenomena agree with those which would result from the assumptions in
the electrical hypothesis.



SB.



ON AN ELECTRICAL CORONA RESEMBLING THE SOLAR

CORONA.



[From the Fifth Volume of the Third Series of " Memoirs of the Literary and
Philosophical Society of Manchester." Session 1871-72.]

(Read February 20, 1872.)

THE object of this paper is to point out a very remarkable re-
semblance between a certain electrical phenomenon (which may have been
produced before, although I am not aware that it has,) and the solar corona.
This resemblance seems to me to be of great importance; for the striking
features of these two coronse are not possessed by any other halos, coronse, or
glories, with which bright objects are seen to be surrounded.

Until the eclipse of 1871 there was considerable doubt how far the
accounts given by observers of the corona could be relied upon ; but
Mr Brothers's photograph has left no doubt on the subject. In this photo-
graph we have a lasting picture of what hitherto has only been seen by
a few favoured philosophers, and by them only during a few moments of
excitement.

This picture shows the beautiful radial structure of the corona, and the
dark rifts which intersect it ; and it also shows the disk of the moon, clear
and free from light. I have not yet seen any of the photographs of the last
eclipse ; but I hear there are several, and that they show the radial structure
and rifts even more distinctly than this one does ; but whether they do or
not, one photograph is positive evidence ; the absence of more simply means
nothing.

The features to which I refer as those which distinguish the solar corona
are:

1. Its rifts and general radiating appearance.



3s] ON AN ELECTRICAL CORONA RESEMBLING THE SOLAR CORONA. 23

2. The crossing and bending of rays.

3. Its self-luminosity, shown by the spectroscopic observations of Professor
Young.

4. The way in which its appearance changes and flickers.

When taken in connection with the blackness of the moon's disk (which
shows that the corona did not exist in, or owe its existence to, matter between
the moon and the plate on which the photograph was taken) these features
show that we see on the card the picture of something which actually existed
in the neighbourhood of the sun that the bright rays, which we see photo-
graphed, were actually bright rays of light-giving matter, standing out from
the sun to an enormous distance. The rifts, and general irregularity of the
picture, show that these rays do not come out uniformly all over the sun's
surface, but that they are partial and local, in some places thinly distributed,
and in others absent altogether. The rays are not all of them straight or
perpendicular to the sun's surface.

Such bright rays as these cannot be the result of the sun's light or heat,
acting on an atmosphere, or on matter circulating in the form of meteorites.
If they are due to the action of the sun's light or heat at all, the matter on
which these act must be distributed in the rays we see ; for the sun's light
and heat coming out uniformly all round, would illuminate any surrounding
matter, if at all, so as to show its figure.

The picture irresistibly calls up the idea of a radial emission. If it is the
picture of distributed matter, that matter must exist in the form of streams
leaving the sun ; if it is the picture of some light-producing action, this also
must exist in the form of an emission from the sun.

Such, then, are the extraordinary features of the solar corona ; and, as
I stated, they resemble those of an electrical corona. Anyone who is familiar
with the various forms of electrical disruptive discharge, will recognize the
general resemblance these coronal features bear to an electric brush. But
to the electrical phenomenon I am about to describe, it is no mere general
resemblance ; it is an actual likeness, with every feature identical.

Before describing this phenomenon, I may be allowed to state how I came
to notice it. It will be remembered that, in a former communication to this
Society, I ascribed the phenomena of comets and the corona to a certain
electrical condition of the sun. Well, the peculiar appearance of Mr Brothers's
photograph induced me to try if a brass ball, brought into the condition
I had ascribed to the sun, would give off a corona presenting this
appearance.



24 ON AN ELECTIUCAL CORONA RESEMBLING THE SOLAR CORONA. [3 B

The phenomenon is produced by discharging electricity from a brass ball,
in a partially exhausted receiver. To do this there is no second pole used,
the objects which surround the outside of the glass probably answering for
this purpose. In order to produce the appearance, a certain relation is
necessary between the pressure of the air and the intensity of the discharge.
It is produced best when the receiver is a glass globe, insulated on a glass
stand, the ball being supported in its middle by a rod (coated with india-
rubber, to prevent any discharge except from the ball). It is only negative
electricity that is discharged into the globe*.

There is great difficulty, even when the apparatus is right, in producing
the corona. Using a large coil, I just exhausted the receiver till the pressure
was equal to half an inch of mercury ; then there was no appearance of a
corona, but one more resembling what is seen in a Geissler tube. I then
let the air in gradually ; and, as the pressure rose, the appearance changed
at first to that of a most extraordinary mass of bright serpents, twining and
untwining in a knot round the ball, then to that of the naked branches of
an oak tree; and as the pressure kept increasing, I gradually observed
amongst the branches a faint corona, which I saw at once was what I was
looking for. It consisted of pencils of light, forming a faint radiating
envelope round the ball, and diminishing in brightness as it receded from it.
The tree gradually died out, until there was nothing left but the bright
radiating envelope, out of which a brighter ray would occasionally flash.
The diameter of this envelope was about three or four times that of the ball.
It was not steady, but flickered, so that at times it appeared to rotate on
the ball. It consisted of pencils, or, as they are termed, bundles of rays,
betweeft which there were dark gaps. These gaps moved round about the
ball ; subsequently, however, by sticking sealing-wax on the ball, I rendered
them definite and permanent. As the pressure of air increased, the brush
became fitful, and finally ceased altogether. It was best when there was
about four inches of mercury in the gauge. The phenomenon could be
produced with different pressures of air, by making a corresponding variation
in the action of the coil ; and hence I assume that there is a definite relation
between the intensity of the charge in the ball, and the pressure of the air
surrounding it, under which the phenomena can occur.

The appearance is very faint so faint that it is difficult to see it even when
close to the ball ; and I find that it takes some time before the eye can fully
appreciate its beauty. It was unfortunately so faint that Mr Brothers was
unable to photograph it. The plate was exposed ten minutes ; but there was
not the slightest trace of anything on it.

* What becomes of this electricity is not clear ; when a machine is used it probably distributes
itself on the inside of the glass, and induces a corresponding charge on the outside. When the
coil is used it must escape back ; for I have had it going for hours without any variation.



3fi] ON AN ELECTRICAL CORONA RESEMBLING THE SOLAR CORONA. 25



The annexed woodcut represents the apparatus employed, except that
the receiver was replaced by the globe described above. The light round
the ball gives a fair idea of the momentary appearance ; and it is impossible
to represent more, as this flickers and changes so rapidly.




2.
3.

4.



This corona has the same special features as the solar corona :
1. The rifts and general radial appearance.

The bending and crossing of rays.

The self-luminosity.

The changefulness and flickering.

There is one point in which it differs from the solar corona ; but this is
no more than must be expected. The shading off of the light in the solar
corona is much more rapid than that in its electrical analogue. If, however,
the pressure of the air could be made to vary, so that it was denser close to
the ball, even this difference could be done away with.

In this experiment, then, we have actually produced the very features
which are so extraordinary in the larger phenomenon ; and were there no



26 ON AN ELECTRICAL CORONA RESEMBLING THE SOLAR CORONA. [3 B

other evidence that the solar corona is electrical, it seems to me that this
resemblance constitutes a very strong proof. When two things existing at
different times, or in different places, resemble each other perfectly, and
resemble nothing else in the range of our knowledge, surely that is high
probability that they are akin.

We may, however, expect, if the sun is electrical, to find some direct
indications of its electricity. Such indications are not wanting, but are
increasing every day. There are the phenomena of the aurora, and the
direct effect of the sun on the electricity of the earth's atmosphere, and on its
magnetism; there is, moreover, the observed connection between the sun-
spots and terrestrial meteorology, as well as the connection between the
planets and the sun-spots, shown by Mr De la Rue and Dr Balfour Stewart.
It must be admitted that these are evident signs of some mutual influence
between the sun and the planetary bodies, which is neither the result of
gravity nor of heat. Almost all these signs are of an electrical character ;
and some are electricity itself; moreover, electricity, or electric induction,
is the only other known "action at a distance" besides gravity and heat.
Is it not, then, probable that this influence is electrical ? Are we to reject
an hypothesis which explains some of these phenomena, and may explain all,
simply because we do not see any cause for the electrical condition of the
sun* why the sun should be charged with negative electricity ?

Should we have discovered that the sun is hot if we had waited to find
out why it was so ? Surely it is sufficient to say that there is no proof that
it is not electrical. But we may go further than this ; for, if we may
compare large bodies with small, then we may show a possible reason for the
sun's being electrified. When two particles of different metals approach or
recede from each other, they become electrified with opposite electricities.
May not the sun be approaching or leaving some other body of a different
material ? I do not suggest this as a probable explanation, but simply in
answer to those who say that it is absurd to suppose the sun can be
electrified.

* This paper was read before Section A of the British Association in 1871, when these
objections were raised.



4.



ON THE ELECTRO-DYNAMIC EFFECT WHICH THE INDUC-
TION OF STATICAL ELECTRICITY CAUSES IN A MOVING
BODY. THIS INDUCTION ON THE PART OF THE SUN
A PROBABLE CAUSE OF TERRESTRIAL MAGNETISM.



[From the Fifth Volume of the Third Series of " Memoirs of the Literary
and Philosophical Society of Manchester." Session 1871-72.]

(Read February 20, 1872.)

IF an electrified body were placed near a moving conductor, so as to
induce an opposite charge in the moving body, this charge would move on
the surface of the conductor so as to remain opposite the electrified body,
whatever the motion might be. If we suppose the moving conductor to
be an endless metal band running past a body negatively charged, the
positive charge would be on the surface of the band opposite to the negative
body, and here it would remain whatever might be the velocity of the band.
Now the effect of the motion of this positive electricity on the conductor,
would be the same as that of an electric current in the opposite direction
to the motion of the band.

If, instead of a band, the moving body consisted of a steel or iron top
spinning near the charged body, the effect of the electricity on the top
would be the same as that of a current round it in the opposite direction
to that in which it was spinning.

It might be that the electricity in the inducing body would produce
an opposite magnetic effect on the top; but even if this were so (and I
do not think it has been experimentally shown that it would be so), its
effect, owing to its distance, would be much less than that of the electricity
on the very surface of the top. If we take no account of the effect of the
inducing body, the current round the top would be of such strength, that



28 ON THE EFFECT OF ELECTRICAL INDUCTION IN A MOVING BODY. [4

it would carry all the induced electricity in the top once round every revolu-,
tion. And if the top were spinning from west to east by south, it would
be rendered magnetic, with the positive pole uppermost that is, the pole
corresponding to the north pole in the earth, or the south pole of the needle.

In order to show that such a current might be produced, a glass cylinder,
twelve inches long and four across, was covered with strips of tinfoil, parallel
to the axis, separated by very small intervals. These strips were about six
inches long and half an inch wide, the intervals between them being the
two-hundredth of an inch. In one place there was a wider interval ; and
from the strips adjacent to this, wires were connected by means of a
commutator with the wires of a very delicate galvanometer. This cylinder
was mounted so that it could be turned at the rate of twelve hundred
revolutions in a minute, and brought near the conductor of an electrical
machine. This apparatus, after it had been thoroughly tested, was found
to give very decided results. As much as 20 deflection was obtained in the
needle ; and the direction of this deflection depended on the direction in
which the cylinder was turned, and on the nature of the charge in the
conductor. When this charge was negative, the current was in the opposite
direction to that of the rotation. It may be objected that the measurement
was not actually made on the cylinder. It must, however, be remembered
that it was made in the circuit of metal round the cylinder, and that my
object was to find the relative motion of the cylinder and the electricity.
Altogether I think it may be taken as experimental proof of the fact
previously stated, that, if a steel top were spinning under the inductive
influence of a body charged with negative electricity, the effect would be
that of a current round the top such as would render it magnetic.

The origin of terrestrial magnetism has not been the subject of so
much speculation as we might have supposed from its importance. This
magnetism seems to have been regarded as part of the original nature of
things, just like gravity, or the heat of the sun, as a cause from which other
phenomena might result, but not as itself the result of other causes.

Yet, when we come to think of it, it has none of the characteristics of a
fundamental principle. It appears intimately connected with other things ;
and when two sets of phenomena have a relation to each other, there is
good reason for believing them to be connected, either as parent and child,
or else as brother and sister the one to be derived from the other, or else
both of them to spring from the same cause.

Now the direction of the earth's magnetism bears a marked relation to
the earth's figure ; and yet it can have had no hand in giving the earth its
shape, which is fully explained as the result of other causes ; therefore we
must assume that the figure of the earth has something to do with its



4] ON THE EFFECT OF ELECTRICAL INDUCTION IN A MOVING BODY. 29

magnetism, or, what is more likely, that the rotation which causes the earth
to keep its shape, also causes it to be magnetic.

If this is the case, then there must be some influence at work, with
which we are as yet unacquainted some cause which, coupled with the
rotation of the earth, results in magnetism. From the influence which the
sun exerts on this magnetism, we are at once led to associate it with this
cause. Yet the cause itself cannot be the result of either the sun's heat,
light, or attraction. What other influence, then, can the sun exert on the
earth ?

The analogy between the magnetism produced in a spinning top, by
the inductive action of a distant body charged with electricity, and the
magnetism in the rotating earth, probably caused by the influence of the
sun, which influence is not its mass or heat, seems to me to suggest what
the sun's influence is. If the sun were charged with negative electricity,
it seems to me to follow, from what the experiments I have described
establish, that its inductive effect on the earth would be to render it
magnetic, with the poles as they actually are.

The only other way in which the sun can act to produce, or influence
terrestrial magnetism, appears to be by its own magnetism. If the sun
were a magnet, it would magnetize the earth. If this is the case, the
sun's poles must be opposite to those of the earth. Now it follows that
such a condition of magnetism would, or at least might, if its materials
are magnetic, be caused by the rotation of the sun under the inductive
action of electricity in the earth and planets, in exactly the same way as
that caused in the earth by the inductive action of the sun. As the
direction of rotation is the same in both bodies, and the electricities of
the opposite kind, the magnetism would be of the opposite kind also. So
that on this hypothesis it is probable that the sun would act by both causes.

When I first worked out this idea, I was not aware that any thing like
it had been suggested before; but Mr Baxendell, after having seen my
experiments, noticed a revieAv of a book On Terrestrial Magnetism, to
which he kindly called my attention. The author, without making any
assumption with regard to the electrical condition of the sun, assumes it to
act on the earth's electricity, precisely as it would under the conditions I
have described ; and he then proceeds to consider, not only the general
features of the earth's magnetism, but all its details (and this in a most
elaborate manner) and to show the explanation which this hypothesis
offers for them, particularly for the secular variation of the direction of the
needle. I am therefore able to speak of the hypothesis as affording an
explanation of the numerous variations of the earth's magnetism, as well
as of its general features.



5.



ON THE ELECTRICAL PROPERTIES OF CLOUDS AND THE
PHENOMENA OF THUNDER STORMS.



[From the Twelfth Volume of the " Proceedings of the Literary and
Philosophical Society of Manchester." Session 1872-73.]

(Read December 10, 1872.)

THE object of this paper is to point out the three following propositions
respecting the behaviour of clouds under conditions of electrical induction,
and to suggest an explanation of thunder storms based on these propositions
and on the assumption that the sun is in the condition of a body charged
with negative electricity : an assumption which I have already made in order
to explain the Solar Corona, Comets' Tails, and Terrestrial Magnetism.

1. A cloud floating in dry air forms an insulated electrical conductor.

2. When such a cloud is first formed, it will not be charged with
electricity, but will be ready to receive a charge from any excited body
to which it is near enough.

3. When a cloud charged with electricity is diminished by evaporation,
the tension of its charge will increase until it finds relief.

I do not imagine that the truth of these propositions will be questioned,
but rather, that they will be treated as self-evident. However, as a matter
of interest I have made some experiments to prove their truth, in which I
have been more or less successful.

Experiment 1 was to show that a cloud in dry air acts the part of an
insulated conductor. The steam from a vessel of hot water was allowed to
rise past a conductor, the apparatus being in front of a large fire, so that
the air was very dry. When the conductor was charged the column of
vapour was deflected from the vertical to the conductor, both for a positive
and negative charge.



5] ON THE ELECTRICAL PROPERTIES OF CLOUDS, ETC. 31



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