Next we have the supposition that the earth's internal heat is due to chemical acBtion, in itself very improbable, except possibly in certain small detached regions of i volcanic activity. It is scarcely necessary to make any farther remark on this than the very obvious one that, if it could be shown that such is really the cause, it is fatal to the Uniformitarian theory, for, in consequence of the steady loss above mentioned, the earth must now contain far less potential energy of chemical affinity than it did ages ago. Obvious as this may appear into the Natural Philosopher, it would seem that some geologists, with Lyell at their head, actually imagine that a species of uniformitarianism may be maintained in the interior by thermo-electric processes; the heat produced by chemical combination being supposed to produce thermo electric currents, and these in turn being employed in decomposing again the products formed, thus giving a perpetual cycle. As Sir W. Thomson remarks, this extraordinary notion "violates the principles of natural philosophy in exactly the same manner, and to the same degree, as to believe that a clock constructed with a self-winding movement may fulfil the expectations of its ingenious inventor by going for ever." If we take the far more probable hypothesis that the internal heat of the earth, like that of the sun, is due mainly to the inpacts of discrete masses falling together from great distances by mutual gravitation, and that now it is merely a hot body cooling according to ordinary laws; it is obvious that by making reasonable assumptions (in the present want of definite experimental data) as to the melting-point of ordinary rock masses, we may determine roughly a superior limit to the time which has elapsed since the superficial strata were in a molten state. This has been done by Thomson, and he finds that 200,000,000 years may have elapsed since the crust consolidated if the melting point of rock be about 10,000° F. (this being an extremely high estimate). If, however, the more reasonable estimate of 7000° F. be taken, this superior limit is reduced to 98,000,000 years. Thomson goes on to show that when once the surface is consolidated, if it do not break up and sink (it contracts, according to Bischoff, 20 per cent. in solidifying) in the lighter fluid below, not many years may have passed before the globe became habitable. In fact, after 10,000 years the rate of increase of temperature downwards would not be more than about 2° F. per foot, a quantity which would produce little effect except on deep-rooted plants; and almost none as regards altera tion of the mean temperature at the surface. It is well to observe, in connexion with these speculations, that Sir W. Thomson seems to prefer to assume that the consolidation took place almost simultaneously throughout the globe; the inner strata tending to consolidate at a far higher temperature than those near the surface, in consequence of the enormous pressure to which they are subjected. This follows as a thermodynamic consequence from the result of Bischoff just quoted. Though the melting point may be raised considerably by pressure, it does not necessarily follow that solidification takes place nearly simultaneously at all depths; so that it is possible that the crust may have solidified long before the interior. What would probably happen in such a case has been graphically described by Thomson as follows: "It is probable that crust may thus form over wide extents of surface, and may be temporarily buoyed up by the vesicular character it may have r tained from the ebullition of the liquid in some places, or, at all events, it may be held up by the viscidity of the liquid, until it has acquired some considerable thickness sufand sink the heavier solid below the lighter ficient to allow gravity to manifest its claim, liquid. This process must go on until the sunk portions of crust build up from the bottom a sufficiently close-ribbed solid skeleton or fra ne, to allow fresh incrustations to remain bridging across the now small areas of lava pools or lakes. "In the honeycombed solid and liquid miss for the liquid, in consequence of its less specific thus formed, there must be a continual tendency gravity, to work its way up, whether by masses of solid falling from the roofs of vesicles of tunnels, and causing earthquake shocks, or by the roof breaking quite through where very thin, so as to cause two such hollows to unite, or the liquid of any of them to flow out freely over the outer surface of the earth; or by gradual sub-idence of the solid, owing to the thermodynamic melting, which portions of it, under intense stress, must experience. according to views recently published by Professor James Thomson. The results which must follow from this tendency seem sufficien ly great and various to account for all that we see at present, and all that we learn from geological investigation, of earthquakes, of upheavals, and subsidences of solid, and eruptions of melted rock." Second. The argument from tidal retardation of the earth's rotation. We have already considered this part of the subject, so far at least, as to show its bearing upon the ques tion of geological time. The discovery of this retardation, as something which really exists and can be measured, in contrast with Kant's pointing out that there is a vera causa, is very curious. The secular acceleration of the moon's mean motion, proved by cal-life under the present conditions-life such as culating back to the recorded eclipses of the we know and can reason abont. When Play3d and 8th centuries B.C., was long a serious fair spoke of the planetary bodies as being perdifficulty to physical astronomers, till Laplace petual in their motion, did it not occur to him to ask, What about the sun's heat? Is the sun first suggested a possible cause in the secular a miraculous body ordered to give out heat and alteration of the eccentricity of the earth's to shine for ever? Perhaps the sun was so orbit. His calculations gave almost exactly created. He would be a rash man who would the observed result; and the question was say it was not-all things are possible to Creasupposed to be settled. Some years ago, how- tive Power. But we know, also, that Creative ever, Adams showed that Laplace's investiga- Power has created in our minds a wish to intion was seriously defective, and that a cor- vestigate and a capacity for investigating; and there is nothing too rash, there is nothing rect analysis reduced his result by half; so audacious, in questioning human assumptions that half of the acceleration of the moon's regarding Creative Power. Have we reason mean motion remained unaccounted for. to believe Creative Power did order the sun to Then the hint given by Kant (which had been recently brought forward independently by Helmholtz, Mayer, J. Thomson, and others) was remembered, and applied to remove the remaining difficulty. It is obvious that, if the earth's rotation be really becom-lowed to investigate here at the surface of ing slower, since it is employed fundamentally in our measurement of time, all other motious must appear relatively accelerated. With reference to this argument, Professor Huxley has committed a singular blunder, in meeting his adversary with a suggestion which is at once and with deadly effect turned against its author. In fact, as Sir W. Thomson says, (( Professor Huxley's hypothesis, if it were valid, would therefore prove retardation by the tides six times as much as that which we have ventured to estimate!" He proceeds to make another and still graver blunder, when he asks, "If tidal retardation can be thus checked and everthrown by other temporary conditions, what becomes of the confident assertion, based upon the assumed uniformity of tidal retardation, that ten thousand million years ago the earth must have been rotating more than twice as fast as at present? Thomson at once shows that this really entitles him to shorten the period which he had before roughly assigned: and he appends a note which, from so quiet and gentle an antagonist, Professor Huxley must look upon as strangely sarcastic, as to the opinion implied in the above extract, that tidal retardation is a temporary condition. A very small amount of mathematical training would have sufficed to preserve so able a man from serious mistakes like these. "The mutual actions and motions of the heavenly bodies have been regarded as if light had been seen and heat felt without any evolution of mechanical energy at all. Yet what an amount of mechanical energy is emitted from the sun every year! If we calculate the exact mechanical value of the heat he emits in 81 of the earth in her orbit round the sun. The days, we find it equivalent to the whole motion motion of the earth in her orbit round the sun has a certain mechanical value; a certain quantity of steam power would be required, acting for a certain time, to set a body as great as the earth into motion with the same velocity. The same amount of steam power employed for the same time in rubbing two stones together would generate an enormous quantity of heat, as much heat as the sun emits in 81 days. But suppose the earth's motion were destroyed, what would become of the earth? Suppose it were to be suddenly, by an obstacle, stopped in its motion round the sun It would suddenly give out 81 times as much heat as the sun gives out in a day, and would "But it is not only to the effect of the tides begin falling towards the sun, and would ac that we refer for such conclusions. Go to oth-quire on the way such a velocity that, in the er bodies besides the earth and moon; consider collision, a blaze of light and heat would be We depend on the sun very much for produced in the course of a few minutes equal the existing order of things. Life on this earth to what the sun emits in 95 years. That is would not be possible without the sun, that is indeed, a prodigious amount of heat; but just Third. The argument from the Sun's Heat. Here again we must quote Thomson, as he has put the argument into an exceedingly compact and comprehensive form : the sun. 18 T consider the result if all the planetary bodies were to fall into the sun. Take Jupiter with its enormous mass, which, if falling into the sun, would in a few moments cause an evolution of 32,240 years' heat. Take them all together-suppose all the planets were falling into the sun-the whole emission of heat due to all the planets striking the sun, with the velocities they would acquire in falling from their present distances, would amount to something under 46,000 years' heat. We do not know these figures very well. They may be wrong by eten or twenty or thirty per cent., but that does not influence much the kind of inference we draw from them. Now, what a drop in the ocean is the amount of energy of the motion of the planets, and work to be done in them before they reach their haven of rest, the sun, compared with what the sun has emitted already! I suppose all geologists admit that the sun has shone more than 46,000 years? Indeed, all consider it well established, that the sun has already, in geological periods, emitted ten, twenty, a hundred, perhaps a thousand-I won't say a hundred thousand-but perhaps a thousand times as much heat as would be produced by all the planets falling together into the sun. And yet Playfair and his followers have totally disregarded this prodigious dissipation of energy. He speaks of the existing state of things as if it must or could have been perennial. () "Now, if the sun is not created a miraculous body, to shine on and give out heat for ever, we must suppose it to be a body subject to the laws of matter (I do not say there may not be laws which we have not discovered) but, at all events, not violating any laws we have discovered or believe we have discovered. We must deal with the sun as we should with any large mass of molten iron, or silicon, or sodium. We do not know whether there is most of the iron, or the silicon, or the sodium certainly there is sodium; as I learned from Stokes before the end of the year 1851; and certainly, as Kirchhoff has splendidly proved, there is iron. But we must reason upon the sun as if it were some body having properties such as bodies we know have. And this is also worthy of attention:-naturalists affirm that every body the earth has ever met in its course through the universe, bas, when examined, been proved to contain only known elements-chemical substances such as we know and have previously met on the earth's surface. If we could get from the sun a piece of its substance cooled, we should find it to consist of stone or slag, or metal, or crystallized rock, or something that would not astonish us. So we must reason on the sun according to properties of matter known to us here. "In 1854, I advocated the hypothesis that the energy continually emitted as light (or radiant heat) might be replenished constantly by meteors falling into the sun from year to year; but very strong reasons have induced me to leave that part of the theory then advocated by me which asserted that the energy radiating out from year to year is supplied from year to year; and to adopt Helmholtz's theory, that the sun's VOL. L. N-16 heat was generated in ancient times by the work of mutual gravity between masses falling together to form his body. The strongest reason which compelled me to give up the former hypothesis was, that the amount of bodies circulating round the sun within a short distance of bis surface, which would be required to give even two or three thousand years of heat, must be so great, that a comet shooting in to near the sun's surface and coming away again, would inevitably show signs of resistance to a degree that no comet has shown. In fact, we have strong reason to believe that there is not circulating round the sun, at present, enough of meteors to constitute a few thousand years of future sun-heat. If, then, we are obliged to give up every source of supply from withoutand I say it advisedly, because there is no submarine wire, no underground railway,' leading into the sun-we see all round the sun, and we know that there is no other access of energy into the sun than meteors,-if, then, we have strong reason to believe that there is no continual supply of energy to the sun, we are driven to the conclusion that it is losing energy. Now, let us take any reasonable view we can. Suppose it is a great burning mass, a great mass of material not yet combined, but ready to combine, a great mass of gun-cotton, a great mass of gunpowder, or nitro-glycerine, or some other body having in small compass the potential elements of a vast development of energy. We may imagine that to be the case, and that he (sic) is continually burning from the combustion of elements within himself; or we may imagine the sun to be merely a heated body cooling; but imagine it as we please, we cannot estimate more on any probable hypothesis, than a few million years of heat. When I say a few millions, I must say at the same time, that I consider one hundred millions as being a few, and I cannot see a decided reason against admitting that the sun may have had in it one hundred million years of heat, according to its present rate of emission, in the shape of energy. An ar iele, by myself, published in Macmillan's Magazine, for March 1862, on the age of the sun's heat, explains results of investigation into various questions as to possibilities regarding the amount of the heat that the sun could have, dealing with it as you would with a stone, or a piece of matter, only taking into account the sun's dimensions, which showed it to be possible that the sun may have already illuminated the earth for as many as hundred million years, but at the same time one also rendered it almost certain that he had not illuminated the earth for five hundred millions of years. The estimates here are necessarily very vague, but yet, vague as they are, I do not know that it is possible, úpon any reasonable estimate, founded on known properties of matter, to say that we can believe the sun has really illuminated the earth for five hundred million years." Professor Huxley endeavours to answer this by attempting to show that Sir W. Thomson, fifteen years ago, "entertained a to tally different view of the origin of the sun's heat, and believed that the energy radiated from year to year was supplied from year to year, a doctrine which would have suited Hutton perfectly." Thomson shows that this assertion is incorrect, and that his view of the entire possible meteoric supply of solar heat, from masses nearer to the sun than is the earth, when properly stated, would give, at the utmost, material for 300,000 years only, at the present rate of dissipation. He carefully guarded himself, in his original paper, from any such charge as that brought by Huxley, for he expressly showed that a meteor supply, such as would annually make up for the sun's loss, if coming from space external to the earth's orbit, would involve such an augmentation of the sun's mass as would within the last 2000 years have dislocated the seasons by a month and a half-the observed dislocation in 2600 years being but an hour and threequarters. And he pointed out that the true test of how much of the sun's loss can be supplied by meteors at present circulating in orbits less than that of the earth is best to be determined by the perturbations of Mercury. These have been examined with great care by Leverrier; and the result is unfavourable to the existence of any supply worth taking into consideration in the study of the question before us, indicating, as it does, an amount of potential energy equivalent only to a few hundred years of solar heat. Hence, as it has been shown by Helmholtz, Thomson, and others, that if the sun's mass had been made up in the most effective manner of those chemical substances known to us, which would give the greatest possible result, the heat of combination of these could not have supplied so much as 5000 years' loss, even at the present rate of radiation; the only theory of solar heat left us is that developed by Helmholtz, which regards the sun as a hot body cooling; the heat having been produced during the falling together of its parts. The specific heat of such a mass, in consequence of the pressure to which it is subject in the interior, must be, according to Thomson's latest estimate, from 10 to 10,000 times as great as that of an equal mass of water under ordinary pressure. These limits are purposely left very wide; and they show that the sun loses by its radiation 1° F. in temperature in a period longer than four years, but less than 4000 years. Thomson ends his reply on this part of the subject with the very sensible remark: "A British jury could not, I think, be easily persuaded to disregard my present estimate by being told that I have learned something in fifteen years." Now it is to be carefully observed, with regard to the three independent lines of argument just explained, that it is no answer to show that each is, from its very nature, somewhat vague in the results which it yields. The argument from the three is not, as Professor Huxley seems to think, only as strong as the weakest of the three; on the contrary, the reasoning is strictly cumulative, and Thomson's position cannot be successfully attacked except by a complete upsetting of at least two of his lines of argument, combined with a great enfeebling of the third. In truth, when we come to examine the question as a whole, giving its full weight to each of the separate details, we find that we may, with considerable probability, say that Natural Philosophy already points to a period of some ten or fifteen millions of years as all that can be allowed for the purposes of the geologist and paleontologist; and that it is not unlikely that, with better experimental data, this period may be still farther reduced. In fact, even Professor Huxley's enlightened concession that a limit of 100,000,000, 200,000,000 or 300,000,000 years requires no complete revolution in geological speculation (though it is matter of notoriety that to Lyell and Darwin, and to the great mass of British popular geologists, such periods would be of little use): -even this concession will soon not satisfy the Natural Philosophers; who, but with the important difference of having right on their side, will soon follow up their advan tage in a manner somewhat resembling the recent behaviour of the great Yankee nation in the matter of the Alabama Claims. elaborate and suggestive as have been all of Thomson's articles, this great question can hardly yet be said to be more than opened; and its future progress rests quite as much with the physical experimenter as with the mathematician. For, At the commencement of this article we borrowed from Milton an account of the concomitants of the preparations for a terrific combat: there we had to stop, as farther quotation might have been personal; we have seen the issue of the fight, and can now sum it up in the words of Horace, which we take to be descriptive of the triumph of Scientific Truth over all assailants, however numerous and powerful : "Sed quid Typhoëus et validus Mimas, In conclusion, as the assailants named by Af Prof. M. HAMMERICH. Kjöbenhavn, 1858. Horace are unfortunately all of the gigantic | 7. Bidrag til en Skildring af Holberg. order, we must supplement the passage by again recurring to our Thersites who writes anonymous nonsense for the Pall Mall Gasette, and who bitterly attacks, without understanding them, the conclusions of one of the greatest philosophers the world has ever seen. That a man should be more ignorant of Cervantes' great novel than is the merest s schoolboy, implies no blame : no more does it imply blame that he should be so ignorant as to consider this question as one of "Mathematics versus Geology," instead of Reasoning versus Unreason; that he should fancy that any disciple of Hutton and Lyell could be content with one or two millions of years: nor even that he should imagine that Sir W. Thomson's arguments concerning an increase of 15 per cent. in the earth's angular ve locity have something to do with the existence of life-all this is his own misfortune; but why should be increase it by publishing his ignorance to the few readers of the Pall Mall Gazette who are able to distinguish between true science and venomous but absurd attempts at smartness? Such a writer does real harm, by preventing the popular extension of true scientific knowledge: and too often, as is the case with the present specimen, tries to hold up to ridicule lofty merit which he is utterly unable to appreciate. No true scientific man could have written as he has done about Sir W. Thomson, certainly not in such a tone, without appending at least his initials. And a genuine littérateur would never have made such an exhibition of himself; but would, in the shrewd words of Professor Huxley, have endeavoured "to gain his cause, mainly by force of mother-wit and common-sense, aided by train. ing in other intellectual exercises." AMONG the authors who appear at comparatively rare intervals in history, as the creators of literary epochs, may fairly be reckoned Ludvig Holberg. The name, "father of modern Danish literature," which is generally bestowed upon him, is a plain indication of the light in which his life and labours have been viewed by the vast majority of his countrymen; and all acquainted with the subject will cheerfully allow that the appellation is well deserved. Before his time, indeed, Denmark, in common with the two other Scandinavian countries, could vaunt her ancient literary treasures, among the noblest of their kind which the world has ever known, the Sagas, and the songs that still charm posterity, that have so often anew inspired the popular heart, and reawakened the slumbering poetic impulse in times of intellectual and spiritual torpor. But long ere the birth of Holberg, or at least ere the period of his first literary activity, the Danish people, like their brethren of the Scandinavian peninsula, had learned to lose, all too readily, the recollection of "that large utterance of the early gods;" and the trumpet voices of the Eddas and the Sagas, which, wild and half-savage though they were, yet rang accordant with the true tones of Nature's poetry, were buried in profound, if temporary, oblivion. The second of the three great periods into which we may divide the history of Danish literature-the "Latin," that succeeded the previous "Icelandic," was now drawing to a close, and, during its protracted course, with the exception of some weak reverberations of the earlier ballad minstrelsy, it could boast of little to attract attention or deserve respect. The east wind of intellectual barrenness was blighting all in Denmark. Men, when they did write, wrote in Latin-hence the name assigned already to the period, and, as a general rule, their lucubrations were of the driest, dreariest kind imaginable. In that special branch of literature which has mainly conferred immortality on Holberg-the department of the Comic Drama,—a beginning doubtless had been made; but what miserable abortions were the attempts of the first Danish Dramatist, Christen Hansen, the Odensee schoolmaster, and his successors, Ranch and Hegelund! Rudeness, vapidity, vulgarity, such were the literary characteris tics of the time. Persons of rank repudiated their native language, and read exclu sively French and German; the literati, such as they were, perused Latin, and wrote Latin solely; here, as Holberg himself ex |