11. The source of terrestrial magnetism, and its connection with solar
activity.
The first and second chapters are devoted to an examination of the
limits of atmospheric expansibility. The experimental investigations
of Dr. Andrews, Mr. Grove, Mr. Gassiot, and M. Geissler are cited to
prove that the expansibility of the atmosphere is unlimited, and other
cosmical evidence is adduced in support of this conclusion.
As this, which is really the foundation of the whole argument, is
directly opposed to the views expressed by Dr. Wollaston, in his
celebrated paper on “The Finite Extent of the Atmosphere,” published
in 1822, and generally accepted as established science, this paper is
reprinted in the second chapter, and carefully examined.
Dr. Wollaston says “that air has been rarefied so as to sustain 1-100th
of an inch of barometrical pressure,” and further, that “beyond this
limit we are left to conjectures founded on the supposed divisibility
of matter; if this be infinite, so also must be the extent of our
atmosphere.”
I contend that our knowledge of the whole subject is fundamentally
altered since these words were written. We are no longer “left to
conjectures founded on the supposed divisibility of matter” to
determine the possibility of further expansibility than that indicated
by 1-100th of an inch of barometrical pressure, as we now have means
of obtaining ten times, a hundred times, a thousand times, or even
an infinitely greater rarefaction than Wollaston’s supposed limit,
an apparently absolute vacuum being now obtainable; and although the
transmission of electricity affords a means of testing the existence of
atmospheric matter with a degree of delicacy of which Wollaston had no
conception, we are still unable to detect any indication of any limit
to its expansibility.
The most remarkable part of Dr. Wollaston’s paper is the _reductio ad
absurdum_ by which he seeks to finally demonstrate the finite extent of
our atmosphere. He maintains, as I do, that if the elasticity of our
atmosphere is unlimited, its extension must be commensurate with the
universe, that every orb in space will, by gravitation, gather around
itself an atmosphere proportionate to its gravitating power, and that,
by taking the known quantity of the earth’s atmosphere as our unit, we
may calculate the amount of atmosphere possessed by any heavenly body
of which the mass is known. On this basis Dr. Wollaston calculates
the atmosphere of the sun, and concludes that its extent will be so
great as to visibly affect the apparent motions of Mercury and Venus,
when their declination makes its nearest approach to that of the sun.
No such disturbance being actually observable, he concludes that such
an atmosphere as he has calculated cannot exist. In like manner he
calculates the atmosphere of Jupiter, and finds it to be so great, that
its refraction would be sufficient “to render the fourth satellite
visible to us when behind the centre of the planet, and consequently to
make it appear on both (or all) sides at the same time.”
On examining these calculations, I have discovered the very curious
error above referred to. As this is a matter of figures that cannot
be abridged, I must refer the reader to the original calculations. I
will here merely state that Wollaston’s method of calculating the solar
gravitation atmosphere and that of Jupiter and the moon leads to the
monstrous conclusion that, in ascending from the surface of the given
orb, we always have the same limited amount of atmospheric matter above
as that with which we started, although we are continually leaving a
portion of it below.
Wollaston’s mistake is based on the assumption that, under the
circumstances supposed, the atmospheric pressure and density, at any
given distance from the centre of the given orb, will vary inversely
with the square of that distance. As the area of the base upon which
such pressure is exerted varies _directly_ with the square of the
distance, the total atmosphere above every imaginable starting-distance
would thus be ever the same. That this assumption, so utterly at
variance with the known laws of atmospheric distribution, should have
remained unchallenged for half a century, and that the conclusions
based upon it should be accepted by the whole scientific world, and
repeated in standard treatises, such as those of the “Encyclopedia
Britannica,” etc., etc., is, I think, one of the most remarkable
curiosities presented by the history of science. If it were merely
a little cobweb in some obscure corner of philosophy, there would
be nothing surprising in its escape from the besom of scientific
criticism; but this is so far from being the case, that it has hung,
since 1822, like a dark veil obscuring another, a wider, and more
interesting view of the universe which the idea of an universal
atmosphere opens out. But I must now proceed to the next stage of the
argument.
Starting from the conclusion reached in the previous chapters, that
the atmosphere of our earth is but a portion of an universal elastic
medium which it has attached to itself by its gravitation, and that
all the other orbs of space must, in like manner, have obtained
their proportion, I take the earth’s mass, and its known quantity of
atmospheric envelope as units, and calculating by the simple rule I
have laid down in opposition to Wollaston’s, I find that the total
weight of the sun’s atmosphere should be at least 117,681,623 times
that of the earth’s, and the pressure at its base equal, at least, to
15,233 atmospheres. What must be the results of such an atmospheric
accumulation?
The experiment of compressing air in the condensing syringe, and
thereby lighting a piece of German tinder, is familiar to all who have
studied even the rudiments of physical science. Taking the formulæ of
Leslie and Dalton, and applying them to the solar pressure of 15,233
atmospheres, we arrive according to Leslie, at the inconceivable
temperature of 380,832° C., or 685,529° F., as that due to this amount
of compression, or, according to Dalton, at 761,665° F. What will be
the effects of such a degree of heat upon materials similar to those
of which our earth is composed?
Let us first take the case of water, which, for reasons I have stated,
should be regarded as atmospheric, or universally diffused matter.
This brings us to a subject of the highest and widest philosophical
and practical importance. I refer to the antagonism between the force
of heat and that of chemical combination, to which the French chemists
have given the name “dissociation.” Having myself been unable to find
any satisfactory English account of this subject at a time when it had
already been well treated by French and German authors, in the form of
published lectures and cyclopædia articles, I assume that others may
have encountered a similar difficulty, and therefore dwell rather more
fully upon this part of my present summary.
It appears that all chemical compounds may be decomposed by heat, and
that, at a given pressure, there is a definite and special temperature
at which the decomposition of each compound is effected. For the
absolute and final establishment of the universality of this law
further investigations are necessary, actual investigations having
established it as far as they have gone, but these have not been
exhaustive.
There appears to be a remarkable analogy between dissociation and
evaporation. When a liquid is vaporized, a certain amount of heat is
“rendered latent,” and this quantity varies with the liquid and with
the pressure, but is definite and invariable for each liquid at a given
pressure. In like manner, when a compound is dissociated, a certain
amount of heat is “rendered latent,” or converted into dissociating
force, and this varies with each compound and with the pressure, but
is definite and invariable for each compound at a given pressure.
Further, when condensation occurs, an amount of heat is evolved, as
temperature, exactly equal to that which was rendered latent in the
evaporation of the same substance under the same pressure; and, in like
manner, when chemical re-combination of dissociated elements occurs, an
amount of heat is evolved, as temperature, exactly equal to that which
disappeared when the compound was dissociated by heat _alone_ under
the same pressure.
According to the recently adopted figures of M. Deville, the
temperature at which the vapor of water becomes dissociated under
ordinary atmospheric pressure is 2800° C., and the, quantity of heat
which disappears, as temperature, in the course of dissociation is 2153
_calorics_, _i.e._, sufficient to raise 2153 times its own weight of
_liquid_ water 1° C.; but, as the specific heat of aqueous vapor is
to that of liquid water as 0·475 to 1, that latent heat expressed in
the temperature it would have given to aqueous vapor is = 4532° C., or
8158° F.
In order to render the analogy between the ebullition and dissociation
of water more evident and intelligible, I will state it as follows:—
To commence the ebullition of To commence the dissociation of
water under ordinary pressure, aqueous vapor under ordinary
a temperature of 100° C., or pressures, a temperature of
212° F., must be attained. 2800° C., or 5072° F., must be
attained.
To complete the ebullition of a To complete the dissociation of
given quantity of water, an a given quantity of aqueous
amount of heat must be applied, vapor, an amount of heat must
sufficient to have raised be applied sufficient to have
the water 537° C., or 968° F., raised the vapor 4532° C., or
above its boiling-point, had it 8158° F., above its dissociation-
not evaporated. point had it not decomposed.
In order that a given quantity of In order that a given quantity of
vapor of water shall condense, the elements of water may combine,
it must give off sufficient heat they must give off sufficient
to raise its own weight of water heat to raise their own
537° C., or 968° F. weight of aqueous vapor 4532°
C., or 8158° F.
I have expressed these generalizations and analogies rather more
definitely than they have been hitherto stated, but those who are
acquainted with the researches of Deville, Cailletet, Bunsen, etc.,
will perceive that I am justified in doing so.[2]
With the general laws of the dissociation of water thus before us,
we may follow out the necessary action of the above-stated pressure
and consequent evolution of heat in the lower regions of the solar
atmosphere upon the large proportion of aqueous vapor which I have
shown that it should contain.
It is evident that the first result will be separation of this water
into its elements, accompanied with a loss of temperature corresponding
to the latent heat of dissociation. We may assume that in the lower
regions of the solar atmosphere the free heat evolved by mechanical
compression will be more than sufficient to dissociate the whole of the
aqueous vapor, and thus the dissociated gases will be left at a higher
temperature than was necessary to effect their dissociation. Their
condition will thus be analogous to that of superheated steam: they
will have to give off some heat before they can _begin_ to combine.[3]
There will, however, be somewhere an elevation at which the heat
evolved by the joint compression of the elementary and combined gases
will be just sufficient to dissociate the latter, and here will be the
meeting surface of the combined and the uncombined constituents of
water. There will be a sphere containing combined oxygen and hydrogen
surrounded by an atmospheric envelope containing large quantities of
aqueous vapor, and the temperature at this limiting surface will be
equal to that of the oxyhydrogen flame under a corresponding pressure.
What will occur under these conditions? Will the “detonating gases”
behave as in the laboratory? Obviously not, as a glance at the third
of the above parallel propositions will show. The dissociated gases
cannot combine without giving off their 4532° of latent heat as actual
temperature. This can only be effected by communication with matter
which is cooler than itself.
If a bubble of steam is surrounded by water maintained at the boiling
temperature, it will not condense at all, because any effort of
condensation would be accompanied with an evolution of heat exactly
sufficient to evaporate its own result. If, however, the surrounding
water is slowly radiating, or otherwise losing its heat, the enclosed
bubble of steam will condense proportionately, by giving off to its
envelope an amount of its latent heat just sufficient to maintain the
water at the boiling-point.
For further illustration, let us conceive the case of a certain
quantity of the elements of water heated exactly to the temperature
of dissociation, and confined in a vessel the sides of which are
maintained externally at precisely the same temperature as the
gases within, so that no heat can be added or taken away from them.
No sensible amount of combination can take place, as the first
infinitesimal effort of combustion, or combination, would set free
just the amount of heat required to decompose its own result. Let us
now suppose a modification of these conditions, viz., that the vessel
containing the dissociated gases, at the temperature of dissociation,
shall be surrounded with bodies cooler than itself, _i.e._, capable
of receiving more heat from it than they radiate towards it; there
would then take place just so much combustion as would set free the
amount of heat required to maintain the temperature of the vessel at
the dissociation-point; or, in other words, combustion would go on to
the extent of setting free just so much heat as the gaseous mass was
capable of radiating, or otherwise transmitting to surrounding bodies;
and this amount of combustion would continue till all the gases had
combined.
We have only to give this hypothetical vessel a spherical form and an
internal diameter of 853,380 miles—to construct its enveloping sides
of a thick shell of aqueous vapor, etc., and then, by placing in the
midst of the contained dissociated gases a nucleus of some kind, we
are hypothetically supplied with, the main conditions which I suppose
to exist in the sun.
A little reflection upon the application of the above-stated laws to
these conditions will show that the stupendous ocean of explosive gases
would constitute an enormous stock of fuel capable, by its combustion,
of setting free exactly the same quantity of heat as had previously
been converted into decomposing or separating force; the amount of
combustion would always be limited by the possible amount of radiation,
and the radiation would again be limited by the resisting envelope of
aqueous vapor produced by this combustion.
If these conditions existed in a perfectly calm and undisturbed solar
atmosphere, there would be a continually increasing external envelope
of aqueous vapor, and a continually diminishing inner atmosphere of
combustible gases; there would be a gradual diminution of the amount of
solar radiation, and a slow and perpetually retarding progress towards
solar extinction.
It should be noted that, according to this explanation, the _supply_
of heat is originally derived from atmospheric condensation due
to gravitation, that the _storage_ of surplus heat is effected by
dissociation, and its _evolution_ mainly by recombination or combustion.
The great difficulty, that of the perpetual renewal of the solar fuel,
still remains unsolved; the fact that during the millions of years of
geological history we find no indications of any declining average of
solar energy is so far still unexplained by this, as by every other,
attempt to account for the origin of solar and stellar light and heat.
In his inaugural address to the British Association Meeting of 1866,
Mr. Grove put the following very suggestive question:—“Our sun, our
earth, and planets are constantly radiating heat into space; so, in
all probability, are the other suns, the stars, and their attendant
planets. What becomes of the heat thus radiated into space? If the
universe has no limit—and it is difficult to conceive one—there is a
constant evolution of heat and light; and yet more is given off than is
received by each cosmical body, for otherwise night would be as light
and as warm as day. What becomes of the enormous force thus apparently
non-recurrent in the same form?”
This is a grand question, a philosophical thought worthy of the author
of “The Correlation of Physical Forces.” Most philosophical thinkers
will, I believe, agree with me in concluding that a sound reply to it
will solve the great mystery of the everlasting radiations of our sun
and all the other suns of the universe. So long as we regard these
suns as the _sources_ of continually expended forces of light and
heat, their everlasting and unabated renewal becomes a mystery utterly
inscrutable to the human intellect, since the creation of new force, or
any addition to the total forces of the universe, is as inconceivable
to us as any addition to the total matter of the universe. The great
solar question assumes a far more hopeful shape when we admit that all
the forces of past radiations are somewhere diffused in space, and
we ask whether a sun contains any mechanism by which it may collect
and concentrate this diffused force, and thus perpetually gather from
surrounding suns as much as it radiates towards them.
The next part of my work is an attempt to show that such a mechanism
does exist in our solar system, and to explain its action.
We know that if atmospheric air is compressed it becomes heated, that
if this heat is allowed to radiate and the air is again expanded to its
original dimensions, it will be cooled below its original temperature
to an extent precisely equal to the heat which it gave out when
compressed. On this principle I endeavor to explain the everlasting
maintenance of the solar and stellar radiations.
The sun is attended by his train of planets whose orbital motion he
controls, but they in return react upon him as the moon does upon
the earth. If this reaction were regular, like that of the moon
upon the earth, a regular atmospheric tide would result; but the
great irregularity of the dimensions, distances, and velocities of
the planets produces a result equivalent to a number of clashing
irregular tides in the solar atmosphere; or, otherwise stated, the
centre of motion and centre of gravity of the whole system will be
perpetually varying with the varying relative positions of the planets,
and thus the solar nucleus and solar atmosphere will be subject to
irregularities of motion, which, though very small relatively to the
enormous magnitude of the sun, must be sufficient to produce mighty
vortices, and thus effect a continual commingling between the outer and
inner atmospheric strata.
It must be remembered that, according to the preceding, the inner or
lower strata of the solar atmosphere should consist of our ordinary
atmospheric mixture of oxygen and nitrogen, and the dissociated
elements of water and carbonic acid, besides some of the more volatile
elements of the solar nucleus. Outside of this there should be a
boundary limit where the dissociated gases are combining as rapidly
as their latent heat can be evolved by radiation; this will form a
shell or sphere of flame,—the photosphere,—and above or beyond this
will be the sphere of vapors resulting from this combustion, which, by
their resistance to radiation, will limit the evolution of heat and
consequent combustion.
Now the vortices above referred to will break through the shell of
combustion, and drag down more or less of the outer vapor into the
lower and hotter regions of dissociated gases.
As there can be no action without equal and contrary reaction, there
can be no vortices, either in the solar atmosphere or a terrestrial
stream, without corresponding upheavals. These upheavals will eject the
lower dissociated gases more or less completely through the vaporous
jacket which restrains their normal radiations, and, thus liberated,
they will rush into combination with an explosive energy comparable
to that which they display in our laboratories; not, however, with an
instantaneous flash, but with a continuous rocket-like combustion, the
rapidity of which will be determined by the possibility of radiation.
The heat evolved by this combustion, acting simultaneously with the
diminution of pressure, will effect a continually augmenting expansion
of these upheaved gases, and as the rapidity of combustion will be
accelerated in proportion to elevation above the restraining vapors, an
outspreading far in excess of that which would be due to the original
upheaving force, is to be expected.
The reader who is acquainted with the phenomena of the solar
prominences will at once perceive how all these expectations are
fulfilled by actual observations, especially by the more recent
observations of Zöllner, Secchi, etc., which exhibit the typical solar
prominence as a stem or jet rushing upwards through some restraining
medium, and then expanding into a cloud-like or palm-tree form after
escaping from this restraint. I need scarcely add that the clashing
tide waves are the _faculæ_, and the vortices the sun-spots.
My present business, however, is to show how these vortices and
eruptions—this down-rush in one part of the solar atmosphere and
up-rush in another—contribute to the permanent maintenance of the
solar light and heat. It must be understood that these outbursts are
only visible to us as luminous prominences during the period of their
explosive outburst, and while still subject to great expansive tension.
Long after they have ceased to be visible to us their expansion must
continue, until they finally and fully mingle with the medium into
which they are flung, and attain a corresponding degree of rarefaction.
This must occur at tens and hundreds of thousands of miles above
the photosphere, according to the magnitude of the ejection. The
spectroscopic researches of Frankland and Lockyer having shown that
the atmospheric pressure at about the outer surface of the photosphere
does not far exceed that of our atmosphere, I may safely regard all
the upper portion of these solar ejections as having left the solar
atmosphere proper, and become commingled with the general interstellar
medium.
If the sun were stationary, or merely rotating, in the midst of this
universal atmosphere, the same material that is ejected to-day would
in the course of time return, and be whirled into the great sun-spot
eddies; but such is not the case; the sun is driving through the ether
with a velocity of about 450,000 miles per twenty four hours.
What must be the consequence of this motion? The sun will carry its own
special atmospheric matter with it; but it cannot thus carry the whole
of the interstellar medium. There must be a limit, graduated no doubt,
but still a practical limit, at which its own atmosphere will leave
behind, or pass through, the general atmospheric matter. There must be
a heaping or condensation of this matter in the front, a rarefaction or
wake in the rear, and a continuous bow of newly encountered atmosphere
around the boundaries in the opposite direction to that of the sun’s
motion. The result of this must be that a great portion of the ejected
atmospheric matter of the prominences will be swept permanently to
the rear, and its place supplied by the material occupying the space
into which the sun is advancing. We are thus presented with a mighty
machinery of solar respiration; some of this newly arriving atmospheric
matter must be stirred into the vortices, its quantity being exactly
equivalent to that of the old material expired by the explosive
eruptions, and left in the rear.
Now, the new atmospheric matter which is thus encountered and inspired,
is the recipient of the everlasting radiations whose destination is the
subject of Mr. Grove’s inquiry; and these, when thus encountered and
compressed, will of necessity evolve more or less of the heat which,
through millions of millions of centuries they have been gradually
absorbing; while, on the other hand, the expired or ejected matter of
the gaseous eruptions will, like the artificially compressed air above
referred to, have lost all the heat which during its solar existence
it had by compression, dissociation, and re-combination contributed to
the solar radiations. Therefore, when again fully expanded, it will be
cooler than the general medium from which it was originally inspired by
the advancing sun.
The daily supply of fresh atmospheric fuel will be a cylinder of
ether of the same diameter as the sun, and 450,000 miles in length!
I have calculated the weight of this cylinder of ether on the
assumption (which of course is purely arbitrary) that the density of
the interstellar medium is one ten-thousandth part of that of our
atmosphere. It amounts to 14,313,915,000,000,000,000 tons, affording a
supply of 165 millions of millions of tons per second; or, if we assume
the interstellar medium to have a density of only one-millionth of that
of our atmosphere, the supply would be rather more than one and a half
millions of millions of tons per second. The proportion of this which
is effective in the manner above stated is that which becomes stirred
into the lower regions of the sun in exchange for the ejected matter of
the prominences.
I will not here dwell upon the bombardment hypothesis, beyond
observing that my explanation of solar phenomena supplies a continuous
bombardment of the above-stated magnitude without adding anything to
the magnitude of the sun.
So far, then, I answer Mr. Grove’s question, by showing that the
heat radiated into space by each of the solid orbs that people its
profundities, is received by the universal atmospheric medium; is
gathered again by the breathing of wandering suns, who inspire as
they advance the breath of universal heat and light and life; then by
impact, compression, and radiation, they concentrate and re-distribute
its vitalizing power; and after its work is done, expire it in the
broad wake of their retreat, leaving a track of cool exhausted
ether—the ash-pits of the solar furnaces—to reabsorb the general
radiations, and thus maintain the eternal round of life.
But ere this, a great difficulty has probably presented itself to the
mind of the reader. He will refer to the calculations that have been
made in order to determine the actual temperature of the solar surface
and the intensity of its luminosity. Both of these are vastly in excess
of those obtained in our laboratory experiments by the combustion of
the elements of water. Even taking into consideration the dissociated
carbonic acid whose elements should be burning in the photosphere
with those of water, and adding to these the volatile metals of the
solar nucleus whose dissociated vapors must, under the circumstances
stated, be commingled with those of the solar atmosphere, and therefore
contribute to the luminosity by their combustion, still by burning here
on the earth a jet of such mixed gases and vapors we should not obtain
any approach to either the luminosity or the temperature which is
usually attributed to the sun.
I have made a very few simple experiments, the results of which
remove these difficulties. They were conducted with the assistance of
Mr. Jonathan Wilkinson, the official gas examiner to the Sheffield
Corporation, using his photometric and gas-measuring apparatus. We
first determined the amount of light radiated by a single fish-tail
gas-burner consuming a measured quantity of gas per hour. We found when
another was placed behind this, so that all the light of the second
had to pass through the first, that the light of the two (measured by
the illuminating intensity of their radiations upon a screen just as
the solar luminosity has been measured) was just double that of one
flame, three flames (still presenting to the photometric screen only
the surface of one) gave it three times the amount of illumination, and
so on with any number of flames we were able to test. Mr. Wilkinson
has since arranged 100 flames on the same, principle, _i.e._, so that
the 99 hinder flames shall all radiate through the one presented to
the screen, thus affording the same surface as a single flame, but
having 100 times its _thickness_ or _depth_, and he finds that the law
indicated by our first experiments is fully verified; that the 100
flames thus arranged illuminate the screen 100 times as intensely as
the single flame. Other modifications of these experiments, described
in Chapter vii. of “The Fuel of the Sun,” establish the principle that
a common hydrocarbon gas flame is transparent to its own radiations,
or, in other words, that the amount of light radiated from such a
flame, and its apparent intensity of luminosity, is proportionate to
its thickness; therefore the luminosity of the sun may be produced by a
photosphere having no greater intrinsic brilliancy than the flame of a
tallow candle, provided the flame is of sufficient depth or thickness.
I see good reasons for inferring that its intrinsic brilliancy is less
than that of a candle—somewhere between that and a Bunsen’s burner.
A similar series of experiments upon the radiation of the _heat_ of
flames through each other, indicated similar results; but my apparatus
for these experiments was not so delicate and reliable as in the
experiments on light, and, therefore, I cannot so decidedly affirm the
absolute diathermancy of flame to its own radiations. Within the limits
of error of these experiments, I found that with the same radiant
surface presented to the thermometer, every addition to the thickness
of the flame produced a proportionate increase of radiation.
This important law, though hitherto unnoticed by philosophers, is
practically understood and acted upon by workmen who are engaged in
furnace operations. Present space will not permit me to illustrate this
by examples, but in passing I may mention the “mill furnaces,” where
armor-plates and other large masses of iron are raised to a welding
temperature by radiant heat, and the ordinary puddling furnace, where
iron is melted by radiant heat. In both of these special arrangements
are made to obtain a “body” or thickness of radiant flame, while
_intensity_ of combustion is neglected and even carefully avoided.
According to this there are two factors engaged in producing the
radiant effect from a given surface, _intensity_ and _quantity_,
_i.e._, _brilliancy_ and _thickness_ in the case of light, and
_temperature_ and _thickness_ in the case of heat. In the Bude light,
for example, consisting of concentric rings of coal-gas, we have small
intensity with great quantity, in the lime-light we have a mere surface
of great brilliancy but no thickness. If I am right, the surface of
the moon maybe brighter than the luminous surface of the sun, the
peculiarities of moonlight depending upon intensity, those of sunlight
upon quantity of light.
The flame that roars from the mouth of a Bessemer converter has but
small intrinsic brilliancy, far less than that of an ordinary gas
flame, as may be seen by observing the thin waifs that sometimes
project beyond the body of the flame. Nevertheless, its radiations are
so effective that it is a painfully dazzling object even in the midst
of sunny daylight; but then we have here not a hollow flame fed only by
outside oxygen, but a solid body of flame several feet in thickness.
Even the pallid carbonic acid flame which accompanies the pouring of
the spiegeleisen has marvellous illuminating power.
The reader will now be able to understand my explanation of the
sun-spots, of their nucleus, umbra, and penumbra. From what I have
stated respecting the planetary disturbances or the solar rotation,
the photosphere should present all the appearances due to the movements
of a fiery ocean, raging and seething in the maddest conceivable fury
of perpetual tempest. If the surface of a river flowing peacefully
between its banks is perforated with conical eddies whenever it meets
with a projecting rock or obstacle, or other agency which disturbs the
regularity of its course, what must be the magnitude of the eddies
in this ocean of flame and heated gases, when stirred to the lowest
depths of its vast profundity by the irregular reeling of the solar
nucleus within? Obviously, nothing less than the sunspots; those mighty
maelströms into which a world might be dropped like a pea into an
egg-cup.
When the photosphere or shell of combining gases is thus ripped open,
the telescopic observer looks down the vortex, which, if deep enough,
reveals to him the inner regions of dissociated gases and vapors. But
these have the opposite property to that which I have shown to belong
to flame; they are opaque to their own special radiations, while the
flame is transparent to the light of the inner portions of itself.
Thus, the dissociated interior of the solar envelope, though absolutely
white-hot, will be comparatively dark (direct experiment has proved
that the darkness of the spots is only relative).
The sides of the vortex funnel will consist of a mixture of dissociated
gases, flaming gases, and combined gases, and will thus present various
thicknesses of flame, and thereby display the various shades of the
penumbra. Space will not permit me here to follow up the details of
this subject, as I have done in the original work, where it is shown
that if the telescope had not yet been invented, all the telescopic
details of spot phenomena might have been described _à priori_ as
necessary consequences of the constitution I have above ascribed to the
sun.
Not merely the great spot phenomena, but all the minor irregularities
of the photosphere follow with similarly demonstrable necessity. Thus
the many interfering solar tides must throw up great waves, literally
mountainous in their magnitude, the summits and ridges of which, being
raised into higher regions of the absorbing vaporous atmosphere that
envelopes the photosphere, will radiate more freely, its dissociated
matter will combine more abundantly, and will thicken the photosphere
immediately below; this thicker flame will be more luminous than the
normal surface, and thus produce the phenomena of the _faculæ_.
Besides these great ground-swells of the flaming ocean of the
photosphere, there must be lesser billows, and ripples upon these,
and mountain tongues of flame all over the surface. The crests of
these waves, and the summits of these flame-alps, presenting to the
terrestrial observer a greater depth of flaming matter, must be
brighter than the hollows and valleys between; and their splendor must
be further increased by the fact, that such upper ridges and summits
are less deeply immersed in the outer ocean of absorbing vapors,
which limits the radiation of the light as well as the heat of the
photosphere. The effect of looking upon the surface of such a wild
fury of troubled flame, with its confused intermingling of gradations
of luminosity, must be very puzzling and difficult to describe; and
hence the “willow leaves,” “rice grains,” “mottling,” “granules,”
“things,” “flocculi,” “bits of white thread,” “cumuli of cotton wool,”
“excessively minute fragments of porcelain,” “untidy circular masses,”
“ridges,” “waves,” “hill knolls,” etc., etc., to which the luminous
irregularities have been compared.
At the time I wrote, the means of examination of the edge of the sun
by the spectroscope was but newly discovered, and the results then
published referred chiefly to the prominences proper. Since that, a
new term has been introduced to solar technology, the “sierra,” and
the observations of the actual appearances of this sierra precisely
correspond to my theoretical description of the limiting surface of
the photosphere, which was written before I was acquainted with these
observed facts. This will be seen by reference to Chapter x., the
subject of which is, “The Varying Splendor of Different Portions of the
Photosphere.”[4]
But I must not linger any further upon this part of the subject,
but proceed to another, where subsequent discoveries have strongly
confirmed my speculations.
The mean specific gravity of the sun is not quite 1½ times that of
water. The vapors of nickel, cobalt, copper, iron, chromium, manganese,
titanium, zinc, cadmium, aluminium, magnesium, barium, strontium,
calcium, and sodium, have been shown by the spectroscope to be floating
on the outer regions of the sun. None of these could constitute the
body of the sun in a solid or liquid state, and be subjected to the
enormous pressure which such a mass must exert upon itself without
raising the mean specific gravity vastly above this; nor is there any
other kind of matter with which we are acquainted which could exist
within so large a mass in a liquid or solid state, and retain so low a
density.
I must confess that my faith in the logical acumen of mathematicians
has been rudely shaken by the manner in which eminent astronomers have
described the umbra or nucleus of the sun-spots as the solid body of
the sun seen through his luminous atmosphere, and the solid surface of
Jupiter seen through his belts, and have discussed the habitability
of Jupiter, Saturn, Uranus, and Neptune always on the assumption of
their solidity, while the specific-gravity of all of these renders this
surface solidity a demonstrable physical impossibility.
If the sun (or either of these planets) has a solid or liquid nucleus,
it must be a mere kernel in the centre of a huge orb of gaseous matter,
and though I have spoken rather definitely of the solar atmosphere in
order to avoid complication, I must not, therefore, be understood to
suppose that there exists in the sun any such definite boundary to
the base of the atmospheric matter as we find here on the earth. The
temperature, the density, and all we know of the chemistry of the sun
justify the conclusion that in its outer regions, to a considerable
depth below the photosphere, there must be a commingling of the
atmospheric matter with the vapors of the metals whose existence the
spectroscope has revealed. Some of these must be upheaved together with
the dissociated elements of water. They are all combustible, and,
with a few exceptions, the products of their combustion would solidify
after they were projected beyond the photosphere. Much of the iron,
nickel, cobalt, and copper might pass through the fiery ordeal of such
projection, and solidify without oxidation, especially when more or
less enveloped in uncombined hydrogen.
It is obvious that, under these circumstances, there must occur a
series of precipitations analogous to those from the aqueous vapor
of our atmosphere. These gaseous metals, or their oxides, must be
condensed as clouds, rain, snow, and hail, according to their boiling
and metal points, and the conditions of their ejection. We know that
sudden and violent atmospheric disturbance, accompanied with fierce
electrical discharges, especially favor the formation of hailstones
in our terrestrial atmosphere. All such violence must be displayed on
a hugely exaggerated scale in the solar outbursts, and therefore the
hailstone formation should preponderate, especially as the metallic
vapors condense more rapidly than those of water on account of the much
smaller amount of their specific heat, and of the latent heat of their
vapors.
What will become of these volleys of solid matter thus ejected with the
furious and protracted explosions forming the solar prominences? In
order to answer this question, we must remember that the spectroscope,
as recently applied, merely displays the gaseous, chiefly the hydrogen,
ejections; that these great gaseous flames bear a similar relation to
the solid projectiles that the flash of a gun does to the grape-shot
or cannon-ball. Mr. Lockyer says: “In one instance I saw a prominence
27,000 miles high change enormously in the space of ten minutes; and,
lately, I have seen prominences much higher born and die in an hour.”
He has recently measured an actual velocity of 120 miles per second
in the movements of this _gaseous_ matter of the solar eruptions, the
initial velocity of which must have been much greater.[5] If such is
the velocity of the gaseous ejections, what must be that of the solid
projectiles, and where must they go?
A cosmical cannonade is a necessary result of the conditions I have
sketched, and as prominence-ejections are continually in progress,
there must be a continual outpouring from the sun of solid fragments,
which must be flung far beyond the limits of the gaseous prominences.
As the luminosity of these glowing particles must be very small
compared with that of the photosphere, they will be invisible in
the glare of ordinary sunshine; but if our eyes be protected from
this, they may then be rendered visible, both by their own glow and
the solar light they are capable of reflecting. They should be seen
during a total eclipse, and should exhibit radiant streams proceeding
irregularly from different parts of the sun, but most abundantly from
the neighborhood of the spot regions. As these spot regions occupy the
intermediate latitudes between the poles and the equator of the sun,
the greatest extensions of the outstreamings should be N.E. and S.W.,
and S.E. and N.W., while to the N., S., E., and W.—that is, opposite
the poles and equator of the sun—there should be a lesser extension.
The result of this must be an approximation to a quadrilateral figure,
the diagonals of which should extend in a N.E. and S.W., and a S.E. and
N.W. direction, or thereabouts. I say “thereabouts,” because the zone
of greatest activity is not exactly intermediate between the poles and
the equator, but lies nearer to the solar equator.
Examined with the polariscope, these radiant streams should display
a mixture of reflected light and self-luminosity. Examined with the
spectroscope, a faint continuous spectrum due to such luminosity of
solid particles should be exhibited, with possibly a few lines due to
the small amount of vapor which, in their glowing condition, they might
still give off. Besides this, there should appear the spectroscope
indications of violent electrical discharges, which must occur as a
necessary concomitant of the furious ejections of aqueous vapor and
solid particles. All these metallic hailstones must be highly charged,
like the particles of vesicular vapor ejected from the hydro-electric
machine, or the vapors and projectiles of a terrestrial volcanic
eruption.
I need scarcely add that this exactly describes the actually-observed
results of the recent observations on the corona, and that all the
phenomena of this great solar mystery are but necessary and predicable
results of the constitution I ascribe to the sun.
There is a method of manufacturing hypotheses which has become rather
prevalent of late, especially among mathematicians, who take observed
phenomena, and then arbitrarily and purely from the raw material
of their own imagination construct explanatory atoms, media, and
actions, which are shaved and pared, scraped and patched, lengthened
and shortened, thickened and narrowed, till they are made to fit
the phenomena with mathematical accuracy. These laborious creations
are then put forth as philosophical truths, and, _afterwards_, the
accuracy of their fitting to the phenomena is quoted as evidence of
the positive reality of the ethers, atoms, undulations, gyrations,
collisions, or whatever else the mathematician may have thus skilfully
created and fitted. It appears to me that such fitness only proves
the ingenuity of the fitter—the skill of the mathematician—and that
all such hypotheses belong to the poetry of science; they should be
distinctly labelled as products of mathematical imagination, and nowise
be confounded with objective natural truths. Such products of the
imagination of the expert may assist the imagination of the student in
comprehending some phenomena, just as “Jack Frost” and “Billy Wind” may
represent certain natural forces to babies; but if Jack Frost, Billy
Wind, electric and magnetic fluids, ultimate atoms, interatomic ethers,
nervous fluids, etc., are allowed to invade the intellect, and are
accepted as actual physical existences, they become very mischievous
philosophical superstitions.
I make this digression in order to repudiate any participation in
this kind of speculation. Though “The Fuel of the Sun” is avowedly a
very bold attempt to unravel majestic mysteries, I have not sought
_to elucidate the known by means of the unknown_, as do these
inventors of imaginary agents, but have scrupulously followed the
opposite principle. I have invented nothing, but have started from
the experimental facts of the laboratory, the demonstrated laws of
physical action, and have followed up step by step what I understand
to be the necessary consequences of these. Many years ago I convinced
myself that our atmosphere is but a portion of universal atmospheric
matter; that Dr. Wollaston was wrong, and that the compression of this
universal atmospheric matter is possibly the source of solar light
and heat; but as this was long before M. Deville had investigated
the subject of dissociation by heat,[6] I was unable to work out
the problem at all satisfactorily. When I subsequently resumed the
subject, I knew nothing about the corona, and had only read of the “red
prominences” as possible lunar appendages, or solar clouds, or optical
illusions. I had worked out the necessity of the gaseous eruptions,
and their action in effecting an interchange of solar and general
atmospheric matter, as the means of maintaining the solar light and
heat, with no idea of proceeding further with the problem, when the
announcement that the prominences were not merely unquestionable solar
appendages, but were actually upheaved mountains of glowing hydrogen,
suddenly and unexpectedly suggested their identity with my required
atmospheric upheavals. It is true that their observed magnitude far
exceeded my theoretical anticipations, and in this respect I have made
some _à posteriori_ adaptations, especially with the aid of a clearer
understanding of the laws of dissociation which almost simultaneously
became attainable.
In like manner, the necessity of the solid ejections presented
themselves before I knew anything of the recently discovered details of
the coronal phenomena—when I had merely read of a luminous halo which
had been seen around the sun, and relying upon Mr. Lockyer, vaguely
supposed it to be an effect of atmospheric illumination. I inferred
that streams of solid particles must be pouring from the sun, and
showering back again, but had no idea that such streams and showers
were actually visible until I was rather startled on learning that the
corona, instead of being, as I had loosely supposed, a mere uniform
filmy halo, had been described by Mr. De la Rue, in his Bakerian
Lecture on the Eclipse of 1860, as “softening off with very irregular
outline, and sending off some _long streams_,” etc. I was then living
on the sides of a Welsh mountain far away from public libraries, and
being no astronomer, my own books kept me better acquainted with the
current progress of experimental than with astronomical science.
Even when “The Fuel of the Sun” was published I knew nothing of the
American observations of the quadrangular figure of the corona, or
should certainly have then quoted them, nor of the fact revealed by
the Eclipse of December, 1870, that, “wherever on the solar disc a
large group of prominences was seen on Mr. Seabroke’s map, there a
corresponding bulging out of the corona was chronicled on Professor
Watson’s drawing; and at the positions where no prominences presented
themselves, there the bright portions of the corona extended to the
smallest distances from the sun’s limb;” and that Mr. Brothers’s
photographs _all_ show the corona extending much further towards the
west than towards the east, the west being “the region richest in solar
prominences.” I am sorry that the limits of this paper will not permit
me to enter more fully into the bearings of the recent studies of the
corona and the prominences upon my explanations of solar phenomena,
especially as the differences between the inner and outer corona, which
still appear to puzzle astronomers, are exactly what my explanation
demands. I must make this the subject of a separate paper, and proceed
at once to the next step of the general argument.
Assuming that such ejections of solid matter are poured from the
prominences, to what distances may they travel? In attempting to
answer this question, I avowedly ventured upon dangerous ground, for
at the time of writing I only knew that the force of upheaval of the
prominences must be enormous, _probably_ sufficient to eject solid
matter beyond the orbit of the earth and even beyond that of Mars.
Actual measurements of the eruptive velocity of the solar prominences
have since been made, and they are so great as to relieve me of my
quantitative difficulty, and show that I was quite justified in the
bold inference that these eruptions may account for the zodiacal light,
the zones of meteors into which our earth is sometimes plunged, and
even the outer zone of larger bodies, the asteroids.
But how, the reader will ask, can such solids, ejected from the
sun, acquire orbital paths around him? “We have been taught that
the parabola is the necessary path of such ejections.” Mr. Proctor
has evidently reasoned in this manner, for in last April number of
“Fraser’s Magazine” he says that some of my ideas are “opposed to any
known laws, physical or dynamical,” that “there is nothing absolutely
incredible in the conception that masses of gaseous, liquid, or solid
matter should be flung to a height exceeding manifold that of the
loftiest of the colored prominences; whereas it is not only incredible,
but impossible, that such matter should in any case come to circle in a
closed orbit round the sun.”
More careful reading would have shown Mr. Proctor that I have
considered other conditions besides those of the textbooks, that the
case is by no means one of simple radial projection from a fixed body
into free space and undisturbed return. I distinctly stated that “the
recent ejections may have any form of orbit within the boundaries of
the conic sections,” from a straight line returning upon itself, due
to absolutely vertical projection, to a circular orbit produced by
the tangential projection of such curving prominences _as the ram’s
horn_, etc. The outline of the zodiacal light would be formed by the
termination or aphelion portion of these excursions, or of such a
number of them as should be sufficient to produce a visible result.
Again, speaking of the asteroids, in Chapter xiv., I state that “I
should have expected a still greater elongation and eccentricity in
some of them, and such orbits may have existed; but an asteroid with
an orbit of cometary eccentricity that would in the course of each
revolution cross the paths of Mercury, Venus, the Earth, and Mars in
nearly the same plane, and dive through the thickly scattered zodiacal
cluster, both in going to the sun and returning from it, would be
subject to disturbances which would continue until one of two things
occurred. Its tangential force might become so far neutralized and
its orbit so much elongated, that finally its perihelion distance
should not exceed the solar radius, when it would finish its course
by returning to the sun. On the other hand, its tangential velocity
might be increased by heavy pulls from Jupiter, when slowly turning
its aphelion path, and be similarly influenced by friendly jerks in
crossing the orbits of the inferior planets; and thus its orbit might
be widened, until it ceased periodically to cross the path of any of
the planets by establishing itself in an orbit constantly intermediate
between any two. Having once settled into such a path, it would remain
there with comparative stability and permanency. If I am right in this
view of the dynamical history of these older ejections, all the long
elliptical paths of zodiacal particles, meteorites, or asteroids, would
thus in the course of ages become eliminated, and the remaining orbits
would be of planetary rather than cometary proportions.”
A little reflection on the above-stated laws of dissociation will show
that the maximum violence of hydrogen explosion will not occur at the
birth of the ejections, but afterwards, when the dissociated gases
have been already hurled beyond the sphere of restraining vapors. If
my explanation is correct, the typical form of a solar prominence
should be that of a spreading tree with a tall stem. At first the least
resistence to radiation and consequent explosive combination must
be in the vertical direction, as this will afford the shortest line
that can be drawn through the thickness of the surrounding jacket of
resisting vapor; but when raised above this envelope, the dissociated
gases, cooled by their own expansion and comparatively free to radiate
in all directions except downwards, will explode laterally as well as
vertically, and thus spread out into a head. My theoretical prominence
will be, in short, a monster rocket proceeding steadily upwards to a
certain extent, and then gradually bursting and projecting its missiles
in every direction from the vertical to the absolutely horizontal.
Should the latter acquire a velocity of about 300 miles per second,
not merely a closed but even an absolutely circular orbit would be
possible. These and the multitude of weaker lateral ejections, reaching
the sun by short parabolic paths, explain the mystery of the inner
corona.
I need only refer Mr. Proctor to his own recently published book on
the Sun, where he will find on plates 4, 5, and 6 a number of drawings
from Zöllner and Respighi, which so thoroughly confirm my necessary
theoretical deductions that they might be a series of fancy sketches of
my own. When we consider that the base of a prominence is only visible
when it happens to start exactly from the limb of the sun, while the
vastly greater proportion of those which are observed, and have been
drawn, have much of the stem cut off from view by the solar rotundity,
the evidence afforded by such drawings in support of my theoretical
deduction, that the typical form of the solar prominences is that of a
palm-tree or bursting rocket, is greatly strengthened.[7]
In a paper by P. Secchi, dated Rome, March 20, 1871, and published in
the “Comptes Rendus,” March 27, this veteran solar observer speaks of
the prominences as composed of jets, which, “upon reaching a certain
elevation, stop and whirl upon themselves, giving birth to a brilliant
cloud.” This cloud is represented as spreading out on all sides from
the summit of the combined jets. Again he says, “It is very common to
see a little jet spot at a certain elevation above the chromosphere,
and there spread itself out into a _wide hat_ (“_un large chapeau_”) of
an absolutely nebulous constitution.” This outspreading nebulosity is
the flash of the incandescent vapors produced by the explosion which is
theoretically demanded by my explanation to occur exactly in the manner
and place described. These expanded incandescent gases will be rendered
visible by the spectroscopic dilution of the continuous spectrum of
the denser photosphere, while the solid projectiles that must proceed
from them in every direction can only be seen during a solar eclipse.
The observations and drawings of Zöllner and Respighi were, for the
most part, made while my book was in the press, and, like those of
Secchi above quoted, were unknown to me when I wrote; I was then
only able to quote, in support of my theoretical requirements, the
evidences of actually observed tangential ejection afforded by Sir John
Herschel’s account of the great solar storm of September 1, 1859.
Besides this direct tangential projection there are other elements
of motion contributing to the same result, such as the whirl of the
prominences on themselves, their motion of translation on the sun’s
disk, and the rotation of the sun itself.
I must now bring this sketch to a close by stating that, in order
to submit the fundamental question of an universal atmosphere to an
_experimentum crucis_ analogous to that by which Pascal tested the
atmospheric theory of Torricelli, I have calculated the theoretical
density of the atmosphere of the moon and of each of the planets, and
compared the results as severely as I could with the observed facts. As
Jupiter is 27,100 times heavier than the moon, and between these wide
extremes there are six planets presenting great variations of mass,
the probabilities of accidental coincidence are overwhelmingly against
me, and a close concurrence of observed telescopic refraction and
other phenomena with the theoretical atmospheric density must afford
the strongest possible confirmation of the soundness of the basis of
my whole argument. Such a concurrence exists, and some new and very
curious light is unexpectedly thrown upon the meteorology of Mars and
the constitution of the larger planets. The latter, if I am right, must
be miniature suns, _permanently_ red or white-hot, must be something
like a photosphere, surrounded by a sphere of vapor (the outside of
which we see), must have mimic spot vortices and prominences, and in
the case of Saturn must eject volleys of meteoric matter, some of which
should finally settle down into orbital paths, and thus produce the
rings.
These are startling conclusions, and when I reached them they were
utterly at variance with general astronomical opinion, but I find since
their publication that some astronomers have already shown considerable
readiness to adopt them. In my case this view of the solar constitution
of the larger planets is not a matter of mere opinion, or guessing,
or probability, but it follows of necessity, and as stated on page
200, “the great mystery of Saturn’s rings is resolved into a simple
consequence, a demonstrable and necessary result of the operation of
the familiar forces, whose laws of action have been demonstrated here
upon the earth by experimental investigation in our laboratories.
No strained hypotheses of imaginary forces are required, no ethers
or other materials are demanded, beyond those which are beneath our
feet and around our heads here upon our own planet; all that is
necessary is to grant that the well-known elements and compounds of the
chemist, and the demonstrated forces of the experimental physicist,
exist and operate in the places, and have the quantities and modes
of distribution described by the astronomer; this simple postulate
admitted, these wondrous appendages spring into rational existence, and
like the eternal fires of the sun, the barren surface of the moon, the
dry valleys of Mercury, the hazy equivocations of Venus, the seas and
continents and polar glaciers of Mars, and the cloud-covered face of
Jupiter, follow as necessary consequences of an universal atmosphere.”
If I am right in ascribing a gaseous condition to the sun and the
larger planets, and tracing the maintenance of this condition to the
disturbing gravitation of the attendant planets or satellites, a
solution of the riddle of the nebulæ at once presents itself. We have
only to suppose a star cluster or group composed of orbs of solar or
great planetary dimensions, and that these act mutually upon each
other as the planets on our sun, or the satellites upon Saturn, but
in a far more violent degree owing to the far greater relative masses
of the reacting elements, and we obtain the conditions under which
great gaseous orbs would be not merely pitted on their surface, but
riven to their very centres, moulded and shaped throughout by the
whirling hurricane of their whole substance. When thus in the centre of
a tornado of opposing gravitations the tortured orb would be twisted
bodily into a huge vorticose crater, into the bowels of which the
aqueous vapor would be dragged and dissociated, and then, entangled
with the inner matter of the riven sphere, would be hurled upwards,
again to burst forth in an explosion of such magnitude that the
original body would be measurably presented as a mere appendage, the
rocket case of the flood of fire it had vomited forth.
The reader must complete the picture. If he will take a little trouble
in doing so he will find that it becomes a portrait of one or the other
of the nebulæ, according to the kind of intergravitating star-cluster
from which he starts. I have endeavored to work out some of the details
of the nebular conditions in Chapter xx. In Chapter xxi. I have
concluded by showing the analogy between a sun and the hydro-electric
machine, the sun being the cylinder and the prominences the steam
jets. If issuing jets of high-pressure steam have the same properties
at a distance of 93 millions of miles from the earth as upon its
surface, the body of the sun and the issuing steam must be in opposite
electrical conditions, and furious electrical excitation must result;
and if the laws of electrical induction are constant throughout the
universe, the earth must be as necessarily subject to solar electrical
influence as to his thermal radiations. Thus the same reasoning which
explains the origin and maintenance of the solar heat and light,
the sun-spots, the photosphere, the chromosphere, the sierra, the
prominences, the zodiacal light, the aerolites and asteroids; the
meteorology of the planets and the rings of Saturn, also shows how the
electrical disturbances which produce the aurora borealis and direct
the needle may originate.
Electrical theories of the corona and zodiacal light, and their
connection of some kind with the aurora borealis, have been put
forth in many shapes, but so far as I have learned none afford any
explanation of the _origin_ of the electrical disturbance. Without this
they are like the vortices of Descartes, which explained the movements
of the planets by supposing another kind of motion still more
incomprehensible.
Explanations which are more difficult to explain than the phenomena
they propose to elucidate only obscure the light of true science, and
stand as impedimente to the progress of sound philosophy.