Helmholtz (“On the Origin of the Planetary System”) says, “It is probable rather that a great part of this heat, which was produced by condensation, began to radiate into space before this condensation was complete. But the heat which the sun could have previously developed by its condensation would have been sufficient to cover its present expenditure for not less than 22,000,000 of years of the past …. We may therefore assume with great probability that the sun will still continue in its condensation, even if it only attained the density of the earth, though it will probably become far denser in its interior, owing to its far greater pressure; this would develop fresh quantities of heat, which would be sufficient to maintain for an additional 17,000,000 of years the same intensity of sunshine as that which is now the source of all terrestrial life.” Of this process of condensation Professor Ball, in his recent work, “In the High Heavens,” says, “It goes without saying that the welfare of the human race is necessarily connected with the continuance of the sun’s beneficent action. We have indeed shown that the few other direct or indirect sources of heat which might conceivably be relied upon are in the very nature of things devoid of necessary permanence. It becomes, therefore, of the utmost interest to inquire whether the sun’s heat can be calculated on indefinitely. Here is indeed a subject which is literally of the most vital importance, so far as organic life is concerned. If the sun shall ever cease to shine, then it must be certain that there is a term beyond which human existence, or indeed organic existence of any type whatever, cannot any longer endure on the earth. We may say once for all that the sun contains just a certain number of units of heat, actual or potential, and that he is at the present moment shedding that heat around with the most appalling extravagance.” Quoting from Professor Langley, he says, “We feel certain that the incessant radiation from the sun must be producing a profound effect on its stores of energy. The only way of reconciling this with the total absence of evidence of the expected changes is to be found in the supposition that such is the mighty mass of the sun, such the prodigious supply of heat or what is the equivalent of heat which it contains, that the grand transformation through which it is passing proceeds at a rate so slow that, during the ages accessible to our observations, the results achieved have been imperceptible …. We cannot, however, attribute to the sun any miraculous power of generating heat. That great body cannot disobey those laws which we have learned from experiments in our laboratories. Of course no one now doubts that the great law of the conservation of energy holds good. We do not in the least believe that because the sun’s heat is radiated away in such profusion it is therefore entirely lost. It travels off, no doubt, to the depths of space, and as to what may become of it there we have no information. Everything we know points to the law that energy is as indestructible as matter itself. The heat scattered from the sun exists at least as ethereal vibration, if in no other form. But it is most assuredly true that this energy, so copiously dispensed, is lost to our solar system. There is no form in which it is returned, or in which it can be returned. The energy of the system is as surely declining as the store of energy of the clock declines according as the weight runs down. In the clock, however, the energy is restored by winding up the weight, but there is no analogous process known in our system.” The purpose of the present work, however, is to clearly demonstrate that just such a process is actually being carried on, and has been so carried on from the beginning, and will be forever. This writer continues reviewing the suppositions formerly entertained, that the sun was a heated body gradually cooling down, or that it was undergoing absolute combustion, and shows that they were utterly insufficient. He then refers to the theory of meteoric supply, of which he says, “It can, however, be shown that there are not enough meteors in existence to supply a sufficient quantity of heat to the sun to compensate the loss by radiation. The indraught of meteoric matter may, indeed, certainly tend in some small degree to retard the ultimate cooling of the great luminary, but its effect is so small that we can quite afford to overlook it from the point of view that we are taking in these pages. It is to Helmholtz we are indebted for the true solution of the long-vexed problem. He has demonstrated in the clearest manner where the source of the sun’s heat lies …. A gaseous globe like the sun, when it parts with its heat, observes laws of a very different type from those which a cooling solid follows. As the heat disappears by radiation the body contracts; the gaseous object, however, decreases in general much more than a solid body would do for the same loss of heat …. The globe of gas unquestionably radiates heat and loses it, and the globe, in consequence of that loss, shrinks to a smaller size …. In the facts just mentioned we have an explanation of the sustained heat of the sun. Of course we cannot assume that in our calculations the sun is to be treated as if it were gaseous throughout its entire mass, but it approximates so largely to the gaseous state in the greater part of its bulk that we can feel no hesitation in adopting the belief that the true cause has been found.”
Regarding the constitution of the sun, it may be stated, however, that we only see its photosphere, which is the visible sun, and the whole volume has a density about that of water; but no man has ever seen the body of the sun itself. In this respect it is like the planet Jupiter: we only know that its density cannot be less than one-fourth the density of the earth’s solid globe. If the photosphere extend to a depth of one thousand, ten thousand, or a hundred thousand miles, the density of the sun’s body or core will be correspondingly increased. Even computing the whole visible volume, the density is far greater than that of any gas we know, even with the solar pressure of gravity; with the sun’s metallic vapors, if the whole core were already vaporized, we would not, to say the least, be likely to observe the sun-spots and other solar phenomena as we find them actually to occur; this, however, will be more fully considered later on. The author continues, “But there is a boundary to the prospect of the continuance of the sun’s radiation. Of course, as the loss of heat goes on the gaseous parts will turn into liquids, and as the process is still further protracted the liquids will transform into solids. Thus, we look forward to a time when the radiation of the sun can be no longer carried on in conformity with the laws which dictate the loss of heat from a gaseous body. When this state is reached the sun may, no doubt, be an incandescent solid with a brilliance as great as is compatible with that condition, but the further loss of heat will then involve loss of temperature …. There seems no escape from the conclusion that the continuous loss of solar heat must still go on, so that the sun will pass through the various stages of brilliant incandescence, of glowing redness, of dull redness, until it ultimately becomes a dark and non-luminous star …. There is thus a distinct limit to man’s existence on the earth, dictated by the ultimate exhaustion of the sun …. The utmost amount of heat that it would ever have been possible for the sun to contain would, according to this authority (Professor Langley), supply its radiation for eighteen million years at the present rate …. It seems that the sun has already dissipated about four-fifths of the energy with which it may have originally been endowed. At all events, it seems that, radiating energy at its present rate, the sun may hold out for four million years or for five million years, but not for ten million years …. We have seen that it does not seem possible for any other source of heat to be available for replenishing the waning stores of the luminary.” He concludes by saying that the original heat may have been imparted as the result of some great collision, the solar body having itself been dark before the collision occurred, and that it may be reinvigorated by a repetition of a similar startling process, but indicates in general terms that such an operation would be bad for the round world and all contained therein. It would, in fact, be rough treatment for even a hopeless case.
Condensation of the solar volume is unquestionably a source of heat, for we know that the solid or liquid interior of the earth increases in temperature at a definite ratio as we descend through its crust; but long before the sun shall have become contracted to the density of the earth all its heat will have become substantially internal heat, and it can then supply no more by radiation to its surrounding planets.
It will be seen that the radiant energy of the sun on any of the above hypotheses is not sufficient to account even for the life period of the earth in the past, and that its future period of energy must be still more brief. Professor Ball (“In the High Heavens”), basing his views on Laplace’s “Nebular Hypothesis,” says, “Looking back into the remote ages, we thus see that the sun was larger and larger the further back we project our view. If we go sufficiently far back, we seem to come to a time when the sun, in a more or less completely gaseous state, filled up the surrounding space out to the orbit of Mercury, or, earlier still, out to the orbit of the remotest planet.” According to this hypothesis, all these brilliant suns, the author says, will “settle down into dark bodies like the earth,” and that “every analogy would teach us that the dark and non-luminous bodies in the universe are far more numerous than the brilliant suns. We can never see the dark objects; we can discern their presence only indirectly. All the stars that we can see are merely those bodies which at this epoch of their career happen for the time to be so highly heated as to be luminous …. It may happen that there are dark bodies in the vicinity of some of the bright stars to which these stars act as illuminants, just in the same way as the sun disperses light to the planets.” One would naturally suppose, however, that there must be some sort of laws to govern such stupendous operations, and that nature is not merely engaged in blowing bubbles. To quote Professor Newcomb: “At the present time we can only say that the nebular hypothesis is indicated by the general tendencies of the laws of nature; that it has not been proved to be inconsistent with any fact; that it is almost a necessary consequence of the only theory by which we can account for the origin and conservation of the sun’s heat; but that it rests on the assumption that this conservation is to be explained by the laws of nature as we now see them in operation. Should any one be sceptical as to the sufficiency of these laws to account for the present state of things, science can furnish no evidence strong enough to overthrow his doubts until the sun shall be found growing smaller by actual measurement, or the nebulæ be actually seen to condense into stars and systems.”
While the validity of the views set forth in the present volume does not depend on the sufficiency or insufficiency of the nebular hypothesis, and in fact requires the condensation as well as the expansion of the solar volume under the influence of heat to be recognized and its extreme importance pointed out, yet it must not be supposed that this great generalization of Kant and Laplace, based on the views presented originally by Sir William Herschel, is established, or that the difficulties in its way are not so enormous as to be almost insuperable. Professor Ball points out that thousands of bodies occupy our solar system, and together compose it as a whole; that these have orbits of every sort of eccentricity and direction, and occupying all possible planes which can pass through the sun; that the bodies circle around the sun, some backward and others forward, and that only the planets seem to conform to some common order; and without this order, which may be accidental, so far as our knowledge goes, the system would have been disrupted long since, if it ever could have begun its operations; and that in this view the heavens may be strewn with wrecks of systems which failed to survive from inherent want of harmony,—that is to say, as based on observation only. Whether the nebular hypothesis be a universal or a partial law of development, or whether the real processes be quite different, cannot, however, depend on the continued maintenance and evolution of the sun’s energy, as this source must in truth be sought for in quite a different direction.
The remaining hypothesis (the seventh) is considered in detail in Professor Proctor’s work, “Mysteries of Time and Space.” The fatal defect in Dr. Siemens’s theory is, that his gases will not be projected from the sun’s equator. Professor Proctor says, “Thus the centripetal tendency of matter at the sun’s equator is very much greater (many hundreds of times greater) than its centrifugal tendency, and there is not the slightest possibility of matter being projected into space from the sun’s surface by centrifugal tendency. Nor is there any part of the sun’s mass where the centrifugal tendency is greater than at the surface near the equator. So that, whatever else the sun may be doing to utilize his mighty energies, he is certainly not throwing off matter constantly from his equatorial regions, as Dr. Siemens’s theory requires.” There are other difficulties which Professor Proctor considers, such as the doubt as to the power of the sun’s rays to disassociate combined gases in space, and also that, since both light and heat must be utilized in this work, if the sun’s energies are to be perpetually renewed, these forces would sensibly disappear in work, and the result would be that the fixed stars would be invisible beyond their domains, and their light, when not totally cut off, would be greatly diminished, in any event, as distances increased, which is not the case. Besides, these gases thus disassociated could never be entirely used by the sun, and the remainder would be wasted, and the part wasted would vastly exceed that utilized, probably in as great proportion of waste as that of the sun’s light not utilized by the planets, which gather but one two-hundred-and-thirty-two-millionths of the whole. It may be further added that these gases would be mechanically mixed, the combined and the disassociated, and this would be mostly the case in those parts nearest the sun, so that large volumes of spent and useless gases would have to be carried in to no purpose whatever. In fact, these gases would gradually form a closed circuit of supply and discharge, and surrounding space would be but slightly affected. Professor Proctor concludes, “We have, in fact, the fallacy of perpetual motion in a modified form.”
It will be apparent that under any single one, or all, of these hypotheses, the future prospect for created forms and continued existence is hopeless, and that the inevitable result must do violence to every conception of either an intelligent creative power or the operations of universal law. The mind revolts from the continued degradation and destruction of all organic creation, while the malevolent and iconoclastic forces of nature hold high revel over final ruin and eternal destruction, brought about by their own incessant efforts, striking out blindly to make or mar, and they alone the deathless survivors, the half-blind fates and furies of the eternal future. It betokens, not the processes of orderly government, but the reign of anarchy.
Note.—Since this work has been in press, at the annual meeting of the British Association, August 8, 1894, Lord Salisbury, the President, delivered a powerful and lucid address on the present status of scientific knowledge and its limitations. With reference to the antiquity of the earth we quote the following: “It is evident, from the increase of heat as we descend into the earth, that the earth is cooling, and we know, by experiment within certain wide limits, the rate at which its substances—the matters of which it is constituted—are found to cool. It follows that we can approximately calculate how hot it was so many million years ago; but if at any time it was hotter at the surface by fifty degrees Fahrenheit than it is now, life would then have been impossible upon the planet, and, therefore, we can without much difficulty fix a date before which organic life on earth cannot have existed. Basing himself on these considerations, Lord Kelvin limited the period of organic life upon the earth to a hundred million years, and Professor Tait, in a still more penurious spirit, cut that hundred down to ten.” If a period of anything like ten million years, even, has been requisite to cool the earth’s surface only fifty degrees in temperature, what time must have elapsed since the terrestrial globe had a temperature high enough to effect the difficult chemical combinations of many of the elements which compose its structure? And even this must have been far less than the vast cycles of time during which original consolidation was effected. Through all these ages the sun must have been pouring out his radiant energy at at least his present rate. Radiation of heat from the earth may have been relatively less rapid from a denser carbon-laden atmosphere in times past than at present, but it never could have been more so. The whole address cited is, indeed, strongly corroborative of the facts upon which the present work is based.