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Russel Wallace : Alfred Russell Wallace (sic)
James Croll, Esq. My dear Sir,--I must apologise for not having written before to thank you for having kindly sent me copies of some of your papers. The last one on "The Old River Channels" was exceedingly interesting. You will see that I have made use of your tables of eccentricity in a paper in Nature; and if you have still any copies of the papers containing those tables, I should much like to have them, for though I have a very scanty practical acquaintance with geology, I am exceedingly interested in all the wider problems with which it deals, and one group of which you have done so much to elucidate.--I remain, dear sir, yours very faithfully, Alfred R. Wallace. * * * Holly House, Barking, James Croll, Esq. Dear Sir,--Thanks for your paper on "The Cause of Motion in Glaciers," which I have read with much interest, though I cannot say I am quite satisfied your explanation is the correct one. The fact that glaciers do move in winter when thickly covered with snow, seems entirely to upset your theory of molecular changes caused by heat, as it does that of Canon Moseley. It seemed to me when I read Canon Moseley's paper that his first error was in considering that the fractures of ice in a glacier are [[p. 248]] shearing at all, in his sense of the word. If I take a piece of ice A,
and by contrary and parallel pressure at a and b cause it to fracture all along the line a b simultaneously, so that one half of it is moved into the position a1 b1, I exert the shearing force as understood by Canon Moseley; but if I take the same or a similar piece of ice B,
and by pressure at c with b as a fulcrum cause a fracture on the line a b, bringing the outer half into the position a1 b1, will it not require a very much less than the shearing force? Now the uneven bottom and sides of a glacier must supply a number of fulcra, and the constant motion of the glacier in an uneven bed must cause unequal tensions and compressions, producing numerous points and lines of least resistance, and to cause a fracture at some point a line of least resistance extending over a few inches or feet, a mass of ice many hundreds of feet thick may act by its weight. Thus a number of small fractures and dislocations may be produced in succession at the ever-varying lines of least resistance by a weight of ice which would be quite sufficient to fracture by shearing or in any other way the whole mass at once. If molecular changes caused the motion of glaciers, then why should there be so many fractures as there are? If the weight of the glacier is insufficient to produce fracture, whence come crevasses? If it is sufficient under favourable conditions to produce the great fissures which sometimes run for a mile and widen into crevasses, surely it can produce the smaller cracks and fissures, which, continually occurring at every changing line of least resistance, and being soon obliterated by regelation, will suffice for the slow and viscous-like motion of a glacier. It would be very important to watch the interior of a plank of ice while bending as in Mr. Matthews' experiment, and see whether this occurred by minute cracks or by molecular change. This could be done by means of [[p. 249]] a beam of light passed through it and condensed on a screen. The cause of the greater motion by day than night, and in summer than in winter, seems simple enough, the action of running water beneath the glacier and in its fissures forming a buoyant cushion for it to move on, and keeping its parts to some extent free. Can it be proved mathematically that the force of gravity is not sufficient for the continual readjustment of the equilibrium of the parts of a glacier by repeated small fractures along lines of least resistance, the weight of large portions of the glacier acting successively to effect these fractures and readjustments of small portions of it? The parallel and simultaneous fracture of a mass of ice termed shearing can never, I think, occur in nature, but angular fracture, produced by unequal pressures on two sides of a fixed point, must be continually occurring. The fact that glaciers are most crevassed and fissured where the greatest change of form occurs, whether by passing through a narrow gorge or down a steep incline, plainly indicates that it is by means of fractures, and not by molecular changes, that the viscous-like flow of a glacier is produced. I was sorry you were not at the British Association meeting. I exhibited a large diagram drawn from your tables of eccentricity, and explained its bearing on climate and the rate of organic change. It excited some interest and caused a pretty good discussion, but a Russian mathematician maintained that all calculations of eccentricity and precession for more than a few 10,000 years were so uncertain as to be of no value whatever, and I wanted you to answer him, as I am not sufficiently acquainted with the subject.--Believe me, yours very faithfully, Alfred R. Wallace. * * * [[p. 271]] The Dell, Grays, Essex, James Croll, Esq. Dear Sir,--Your note sent to Dorking has been redirected here from London. The paper you are so kind as to send me may not arrive, so perhaps you will send me another. Mr. Herbert Spencer will be found at the Athanæum Club, Pall Mall, and Mr. George Mivart at 7 North Bank, Regent's Park, London, N.W. I shall read your paper with very great interest.--Believe me, yours very faithfully, Alfred R. Wallace. * * * [[p. 334]] Waldron Edge, Duppas Hill, Croydon, James Croll, Esq. My dear Sir,--Your kind letter was very welcome to me, especially as it also conveys to me Mr. James Geikie's approval of my article. Well knowing my want of practical acquaintance with the phenomena of glaciation, I feel that it is presumptuous in me to write judicially on so complex a subject. My excuse is that for many years the question has been one of the intensest interest to me, and I have taken every opportunity of studying the chief writings bearing upon it. I can only hope that I have fallen into no serious errors [[p. 335]] or misstatements such as dabblers in subjects that don't belong to them are always liable to. I shall take it as a favour if you will point out without hesitation any statements, whether of fact or of theory, that you think require correction, as the chief part of the article will be embodied in a chapter of a work I am now preparing on the causes which have affected the dispersal of animals. Perhaps you can ascertain from some of the Edinburgh meteorologists whether there are any connected observations of the amount of solar radiation on or near the equator, so as to show how far the difference of the sun's distance at perihelion and aphelion makes itself apparent. It appears to have no effect on the temperature of the atmosphere, but it certainly ought on the direct radiation, and it would be a most important guide to know what effect it really has. I am a great admirer of the late Mr. Belt's writings, and long held to his view as to the causes of glaciation, but on fuller consideration gave them up. I am still, however, greatly fascinated by his theory of the blocking up of the drainage of continents by ice to explain the wide spread of loess and gravel. The ordinary explanations seem utterly inadequate if the facts stated in Belt's papers are anywhere near true. I can hardly accept, however, the mid-Atlantic glacier from Greenland to the Bay of Biscay. Might it not be possible that the confluent glacier of Norway, Scotland, Ireland, and Wales blocked up the North Sea and English Channel? This, with some elevation of the land and some lowering of the ocean, might give almost as much "damming up" as seems needful in Europe.--Believe me, yours very faithfully, Alfred R. Wallace. * * * [[p. 336]] Waldron Edge, Duppas Hill, Croydon, James Croll, Esq. My dear Sir,--I know so little of meteorology that I should prefer not to write to Nature on the subject. If you or Mr. Buchan would do so, it would, I am sure, receive more attention. I should think Quito would be the best place for such observations, as I fancy the atmosphere is pretty [[p. 337]] clear all the year round, and there must be some European residents who could make such observations if instructed. But could not valuable results be obtained at some of our regular meteorological observatories, such as Bombay, by taking a series of black bulb observations in July and January at equal altitudes of the sun, and with equal transparency of the air. The latter factor might, I should think, be determined sufficiently by observing the colour of the sky, as uncondensed vapour is, I believe, quite diathermous to direct rays. Of course, to make the observations comparable, the temperature of the air should also be equal, but a correction for this might probably be arrived at. Am I not right in supposing that observations made at any latitude in July and January, with the same altitude of the sun, the same transparency of atmosphere, and the same temperature of air, ought to give the results we require, and though the extreme differences of air temperature in our latitude in July and January might prevent any good results being obtained, that would not be the case within the tropics. Neither at Bombay nor at Batavia, where there are regular meteorological observatories, do they seem to make a single observation of direct sun heat. Mr. Buchan would be the proper person to call attention to this, and to show the interesting physical problems which a series of such observations would help to solve.--Believe me, yours very faithfully, Alfred R. Wallace. * * * Waldron Edge, Duppas Hill, Croydon, James Croll, Esq. My dear Mr. Croll,--I have been expecting with much interest to see your promised communication to Nature on the cause of the absence of change in the temperature of the equator at aphelion and perihelion. [[p. 338]] I sincerely hope ill health may not be the cause of your silence on the subject. This, however, is not what I am now writing about. In the last few pages of my article in the Quarterly I touch very briefly on the great difficulty of the alternation of climate theory, the total absence of all indications of severe cold in the Arctic or Temperate regions, from the Miocene backward throughout all geological time. It is a difficulty that must not be shirked; for if the theory be the true one, I believe that some indications of the fauna and flora of these constantly recurring cold periods must exist, and can be found if sought for, especially during the later Secondary or earlier Tertiary formations. Your connection with the Geological Survey will probably enable you to direct me where to look for such indications with the best chance of finding them,--I mean in what works; or you may know some geologist who has worked at some extensive group of deposits in such detail as to be able to give the required information directly. It seemed to me that what is to be expected is, that in any extensive series of conformable strata of, say Eocene or Cretaceous age, there ought to occur at tolerably regular intervals a series of beds somewhat distinct in lithological character, and in which the usual fossils of the formation are either absent or partially replaced by dwarfed forms. Such beds might sometimes be very thin and insignificant, owing to the scanty deposition during an epoch when the bed was completely glaciated. If any one such case can be found, either in this country or in a more northern latitude, it would give an immense support to the theory. You probably know if there are any of the geologists of the Survey who hold the theory firmly and have looked out for such evidences; or, if not, you can no doubt refer me to some one who can give me information on the subject, or to some work which gives the details of a series of beds and their fossils where such evidence is likely to be found. Do not put yourself to any inconvenience to reply [[p. 339]] to this letter until it is quite agreeable for you to do so.--Believe me, yours very faithfully, Alfred R. Wallace. * * * [[p. 358]] Pen-y-bryn, St. Peter's Road, Croydon, James Croll, Esq. Dear Mr. Croll,--Many thanks for your interesting letter. The facts you mention are most curious and startling, and I shall look with great interest to Professor Geikie's detailed account of them. My chapter on "Glacial Epochs and Warm Polar Climates" has passed through the press some months back, and I am now near the end of my book. I can hardly venture to hope that my conclusions will satisfy you, but I may say here that they have been reached mainly by giving greater weight to your admirable views on ocean currents as affecting climate, than you seem to do yourself. I have endeavoured to show that a comparatively slight increase of the warm tropical waters carried to the Arctic regions, combined with somewhat less high land in those regions, would render glacial conditions impossible there, and this being done, there would necessarily result the state of climate that the Miocene Arctic vegetation showed did exist. I have further attempted to prove that the geological evidence shows that there was, during the greater part of the Secondary and Tertiary periods, such terrestrial conditions as would cause this great transference of equatorial heat northwards, and I have further argued, I hope soundly, that, such a condition of things existing, neither high eccentricity nor the changing phases of aphelion and perihelion would alter the general character of the climate, though it might affect the nature of the seasons. I also show that the changing phases of perihelion, etc., would only reverse the Polar glaciation when that glaciation was of small extent. When it was extensive and excessive, the change to winter in perihelion would not do away [[p. 359]] with the Glacial epoch, but only cause a slight fluctuation of its southern limits. This will enable you to form some idea of the nature of my argument, which I am sure you will weigh carefully when I have the pleasure of sending you a copy of the book, as I hope to do in a few months.--Believe me, yours very faithfully, Alfred R. Wallace. * * * [[p. 361]] Pen-y-bryn, St. Peter's Road, Croydon, James Croll, Esq. My dear Sir,--I am very sorry to hear of your continued ill health, so far as regards mental work. I trust, however, that you may be spared the affliction of paralysis, and may soon quite recover. Personally I should much regret losing the benefit of your criticism of my theory of geological climate, which is really founded almost wholly on your own researches, and which so very few people seem able clearly to comprehend.--With best wishes, believe me, yours faithfully, Alfred R. Wallace. * * * [[p. 382]] Frith Hill, Godalming, Dear Mr. Croll,--I have much pleasure in signing your memorial, and sincerely hope you may be successful, as I think you have been very badly treated. I read your article in the British Quarterly yesterday. It is very forcible and well reasoned, yet I doubt if it will produce much effect. The extreme materialists will reply that matter and its forces being eternal and infinite, all the motions of matter necessary to produce organised beings have been determined by preceding motions, back to all eternity. They will maintain that these conceptions of eternal matter and forces are no more difficult than the conception of a determining power, which is neither matter nor force. I am very glad to hear you are better. Have you read Stallo's Concepts and Theories of Modern Physics, one of the International Scientific Series? It contains some most acute criticisms of modern scientific views, especially of the kinetic theory of gases and of non-Euclidean geometry. I think you would be interested in it.--With best wishes, yours faithfully. Alfred R. Wallace. * * * [[p. 387]] Frith Hill, Godalming, Dear Mr. Croll,--I am glad to see you have such an array of signatures to your memorial. It must surely receive attention. I shall be glad to read your article again, though I think I fully see the drift of your argument. No doubt force alone is no explanation of anything, but all materialists begin with definite forces acting according to definite laws, and the whole question is whether, these definite forces being infinite or practically infinite in number, the atoms of physicists would not by their interaction through infinite time produce all the results of the material universe without any further "determinism" than that implied in the definite nature of the original forces. This view, if I remember rightly, you do not discuss, and it affords a complete answer to some of your arguments. Is not this so?--Yours very truly, Alfred R. Wallace. * * * [[p. 440]] Frith Hill, Godalming, Dr. James Croll, F.R.S. Dear Mr. Croll,--I have been reading, with very great interest and pleasure, the two last chapters of your book on the origin of sun's heat and of nebulæ. Your [[p. 441]] theory of the light and heat of all suns, stars, and nebulæ being due to arrested motion seems to me most simple, suggestive, and probable, and supported by a mass of weighty fact and argument. It seems the complement of the molecular theory of gases, the molecules in this case being the vast molar masses of the stellar universe. There is, however, a point connected with your discussion of the age of the sun's heat and of geological time that does not seem to me so clear. You say that the sun can only have been giving heat at the present rate for 20 million years if heat is due solely to gravitation, and that geology requires far more than 20 million years. Your arrested motion gives any possible amount of heat to begin with, and thus you get a longer period of emission. But this seems to me rather beside the point. Whatever heat the sun originally had, it had cooled down to the present temperature by radiation, losing heat less and less rapidly as it became cooler. In doing so, it must have passed through the point at which life, such as we find in the earlier Palæozoic rocks, first became possible, say a temperature such as would have heated the ocean to 120º or 150º F. Would not the time from that epoch to now be a fixed period, whatever the primitive heat of the sun? If so, this period is what we want to arrive at, not the whole period during which the sun has been giving out heat, which has no bearing on the problem. Thus let H be the heat of the sun at starting, H - N the heat now. It has cooled according to some definite law. H . . H - a . . H - 3 . . H - c . . . . . . H - N If H - c represents the temperature at which life became possible on earth, then the time H - c . . . to H - N is what we want, and whether the time between H and H - c was 5 million or 5000 million years makes no difference whatever. Another limiting factor is the time required for the earth to cool from the highest possible life temperature to present temperature. This [[p. 442]] you allude to at end of Chapter xviii. as not calculable within sufficiently close limits, but you do not, I think, refer to the fact that the time of the sun's cooling, from the limits of terrestrial life temperature to present temperature, is not affected by the total store of its original heat. This point seems to me to want further elucidation.--Yours very faithfully, Alfred R. Wallace. * * * [[p. 468]] Parkstone, Dorset, James Croll, Esq. My dear Sir,--I have now been able to read your very interesting Stellar Evolution. I think your general idea of the stellar universe a very probable and suggestive one, as it accounts for the proper motion of the stars and other phenomena, which a general nebulous theory will not do. But I do not think that this theory in any way gets over the difficulty of the amount of solar heat and the duration of geological time. You appear to have overlooked the fact that the initial heat of the solar nebula has no hearing on the question at all, but only the heat at the time when it (the nebula) had contracted to the diameter of the earth's orbit and had thrown off the earth. Now, the heat at that epoch is a fixed quantity, not affected by the initial heat of the nebulæ. It matters not, therefore, whether the original heat of the solar system was sufficient to expand the solar nebula to the diameter of the orbit of Neptune, or to ten times that diameter; when it had cooled down to the dimensions of the earth's orbit, it would have reached the same temperature and have contained the same store of heat. What we require is not a greater original heat, but some agency by which the sun continued to generate heat, if not so fast as it gives it out, yet sufficiently to delay the cooling almost indefinitely. Two such causes are [[p. 469]] conceivable and have been suggested,--one derived from the constant rain of meteorites on the sun from the stellar space through which it passes during its proper motion through the stellar universe; the other the continued absorption of fresh gaseous matter from the ethereal spaces it is passing through--as suggested by Mr. Matthew Williams in his Fuel of the Sun. This objection seems to me so obvious that I cannot understand how it is you have not even noticed it. For your purpose it was necessary to show that, after the earth had been thrown off, and its surface had cooled sufficiently to allow of the condensation of water and the formation of sea and land, the sun could possibly contain many times more heat than was required to keep it at the diameter it had then attained. You must show, in fact, that it is possible to have two suns, identical in constitution, in mass, and in dimension, yet one containing many times as much heat as the other, because it had had a higher initial temperature. That seems to me to be physically impossible. Is it not so?--Yours very faithfully, Alfred R. Wallace. * * * [[p. 470]] Parkstone, Dorset, Dear Mr. Croll,--You seem to assume that in the nebular hypothesis the primitive nebula is assumed to be cold, and its condensation to be due solely to gravity. But did anybody ever hold this theory? I find in the article "Solar System" in the English Cyclopædia written by Professor D. Morgan, the theory is stated to be that "condensation takes place arising from loss of heat," and again he refers to the necessary consequences "of the cooling of a nebulous atmosphere." And, surely, any other conception is absurd and physically inconceivable. Can anybody suppose the whole physical constitution of the universe to be so different from what it is now, that iron and all the other metals and solid elements could exist as cold vapours. The point of liquefaction of each metal, as well as the points of vaporisation of every solid element, are physical constants, and cannot be conceived to have been totally different from what they are now in any rational theory of the universe. [[p. 471]] I cannot therefore see that the theory of a "cold nebula," not leading to heat enough to produce the sun or the solar nebula by gravitation alone, has any bearing on the problem. The sun, at a certain epoch, say that of the Laurentian epoch, had condensed to a certain diameter, and it has since condensed to the diameter it now possesses. Each of these diameters, assuming the mass to be a fixed quantity, implies a definite amount of heat, which amount would not be affected by the fact of the original nebula having been hotter, and therefore larger, or cooler, and therefore smaller, since it must anyhow have been once at least as large as to fill the orbit of Neptune. This objection your letter does not touch. I return Dr. Huggins' paper, which I had seen in Nature.--Believe me, yours faithfully, Alfred R. Wallace.
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