Science in Short Chapters — The Fuel of the Sun, Part I

THE FUEL OF THE SUN.

I offer the following sketch of the main argument which is worked out more fully in the essay I published in January, 1870, under the above title, hoping that many who hesitate to plunge into a presumptuous speculative work of more than 200 octavo pages may read this article, and reflect upon the subject.

The book has been handled in a most courteous and indulgent spirit by all the reviewers who have noticed it, but none have ventured to grapple with the argument it contains, although every possible opportunity and provocation for doing so is designedly afforded.

It all rests upon the question which is discussed in the first three chapters, viz.

, whether the atmosphere which surrounds our earth is limited or unlimited in extent?

If my reasoning upon this fundamental question is refuted, all that follows necessarily falls to the ground.

If I am right, all our standard treatises on pneumatics and meteorology, which repeat the arguments contained in Dr. Wollaston’s celebrated paper, must be remodeled.

At the outset, I reprint that paper, and point out a very curious and monstrous fallacy which, for half a century, remained undetected, and had been continually repeated.

As the main point of issue between myself and Dr. Wollaston is merely a question of very simple arithmetic and geometry, nothing can be easier than to set me right if I am wrong; and, as the philosophical consequences depending upon this issue are of vast and fundamental importance, the question cannot be ignored by those who stand before the world as scientific authorities, without a practical abdication of their philosophical responsibilities.

Any man who publishes an astronomical or meteorological treatise without discussing this question, which stands before him at the threshold of his subject, is unfit for the task he has undertaken, and unworthy of public confidence.

This may appear a strong conclusion just now, but a few years will be sufficient to graft it firmly into the growth of scientific public opinion.

[1] “The Fuel of the Sun” is simply an attempt to trace some of the consequences which must of necessity result from the existence of an universal atmosphere, and it differs from other attempts to explain the great solar mystery, by making no demands whatever upon the imagination, _inventing_ nothing,—no outside meteors, no new forces or materials.

It supposes nothing whatever to exist but the known facts of the laboratory—the familiar materials of the earth and its atmosphere.

It is shown that these materials and the forces residing within them must of necessity produce a sun, and manifest eternally all the observed solar phenomena, provided only they are aggregated in the quantities which our own central luminary presents, and are surrounded by attendant planets, such as his.

Nothing is assumed or taken for granted beyond the simple fundamental hypothesis that the laws of nature are uniform throughout the universe.

The argument thus conducted leads us step by step to a natural and connected explanation of the following important phenomena:— 1. The sources of solar and stellar heat and light.

2. The means by which the present amount of solar heat and light must be maintained so long as the solar system continues in existence.

3. The origin of the general and particular phenomena of the sun-spots.

4. The cause of the varying splendor of the photosphere, including such details as the “faculæ,” “mottling,” “granulations,” etc. , etc. 5. The forces which upheave the solar prominences.

6. The origin of the corona and zodiacal light.

7. The origin of the meteorites and the asteroids.

8. The meteorological phenomena of the planets.

9. The origin of the rings of Saturn.

10. The origin of the special structure of the nebulæ.

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.