« ПредыдущаяПродолжить »
logarithms of radius vector, change of midwinter heat com. pared with a mean distance, and results for Great Britain.
In A.D. 1800 the excentricity is .01678, the anomaly 98°, log. of radius vector in midwinter .00623, the increase + 69.77 and 390 60.77= 320.23 is the midwinter heat of Great Britain, in a circular orbit, to be added to the degrees in col. 5, to obtain the midwinter heat on Mr. Croll's hypothesis, after due corrections.
46. Thus it appears, when the principle of Mr. Croll's calcu. lation is admitted, and necessary corrections are introduced, the midwinter depression, or increase of cold in Great Britain, at his earlier date, B.C. 850,000, would not be 450.3, but only 100:6; and that in B.C. 210,000 there would not be a decline of 37°•7, but a rise of 21°:6. At B.C. 220,000 there would be a decline of 20°.3; and this is fourteen degrees less than the amount in his theory. And when we observe, further, that the same principle would involve the consequence, that southern winters should now be 13° colder than at tho same latitudes in the northern hemisphere, while there is actually only a very slight difference, the disproof of the hypothesis seems tolerably complete.
47. The way to restore some semblance of truth to the theory is to apply it, not to the periods in round numbers in the table, but to intermediate dates, when the solstice was really in the aphelion. This is nearly fulfilled for the date B.C. 220,000, but neither for B.C. 850,000 nor B.C. 210,000. Indeed at the latter date the winter solstice is almost exactly in the perihelion, and by the hypothesis the midwinter heat would be 21° higher than now, instead of 38° lower. In the other case the solstice has the anomaly 1260.22,' by the approximate reckoning. The rate of change is 1390.50 + 29:47=
1690-37 for 10,000 years. To bring it to 60°, which is nearly the position of maximum effect, would require an interval of 3,900 years, or a date from A.D. 1800 backward, of 846,100 years. The corrected exentricity would then be about .06476, instead of .0664 or 0747. The depression, by the corrected rule, at this the most favourable moment, since the logarithm of the radius vector at the aphelion would be *02725, will represent a diminished heat, compared with a circular orbit, of 29o.58, or 29.7 F., and this will be counteracted by a summer heat, exceeding the present by 240.8 F., or an average of 89o.
48. The other periods most favourable to the effect of depressing the northern winters will be, reckoning backward from A.D. 1800 as before.
823,000 diminution from present winter heat 28°:4 result 10:6
Now, when we remember that the approach to the maximum would last only one or two thousand years; that the summer, in each case, would be hotter than at present by all the contrast hetween the present aphelion and the past perihelion distance; that the heat annually received by the northern hemisphere at these periods is 3 or 4 per cent. above the mean amount; and that the actual difference of the northern and southern winters, which by the same scale should be 130.7, or nearly half the whole amount, is in reality hardly sensible, I think the presumptive evidence is irresistible in favour of the view of Sir J. Herschel, Arago, and others, which Mr. Croll reverses as erroneous; that the differences of excentricity, within their actual limits, will by no means account for the occurrence of glacial periods.
49. There is another hypothesis, wholly distinct from that of Mr. Croll, which seems to me to admit of being confirmed by very strong presumptions. It is that which refers the main stages of geological change to marked eras of chemical transmutation, in the latest stages of terrestrial condensation. But this cannot be unfolded at the close of a paper which has already reached rather an undue length.
I think I have sufficiently shown that the chief definite grounds, of astronomical science, upon which the doctrine of man's extreme antiquity has been assumed to rest, are wholly fallacious and unsound,
The CHAIRMAN (C. Brooke, Esq., M.D., F.R.S.).-I am sure that we all u nite in returning our best thanks to Professor Birks for the very able paper which he has read.* It is now open for those present to make observations thereon.
Rev. Prebendary Currey, D.D.-I feel incompetent to enter upon the details of the arguments which have just been presented to us with reference to the special theories which Professor Birks has discussed; in fact, the accumulation of scientific research and of learning in his paper has been so great as wholly to bewilder me. But what I want to point out is this, that the question before us is “modern cosmogonies examined in their bearing upon the antiquity of man," and I confess that to me it is very difficult to understand what bearing a great deal of this paper has upon the subject of the antiquity of man. Let us suppose for a moment that all the concluisions which Professor Birks seeks to set up are clearly established, and that all the theories which he attacks are completely overthrown, still, in my opinion, that would not affect the question of the antiquity of man. All that it would do would be to show us that certain theories put forward by particular philosophers are liable to exception, and are, perhaps, unsound; but it would not necessarily follow that other theories may not be quite sound. The destruction of each theory can only affect such others as proceed upon similar lines ; and even those only so far as they concern the subject in hand. Professor Birks's arguments have to do with the antiquity of the earth, rather than with that of man. Now if you can prove that certain strata, containing the remains of man, are not so old as has been represented, you may make it probable that man has not been so old an inhabitant of the earth as some suppose. The paper does not refer to any special antiquity of man,
* Since the meeting Mr. Brooke has sent the following observations, which he intended to have made towards the close of the discussion :
“I wished to have made a remark, had time permitted, on § 13 of Professor Birks's paper. I cannot see that, “the hypothesis that the heat transferred from a hot to a cool body is strictly as the difference of their tenperatures, and that the temperature is the quotient of the heat in any body divided by the mass,' implies the corpuscular theory of heat. Speaking logically, it must be borne in mind that heat has no objective existence; it is a subjective impression on the organs of sensation produced by certain molecular wave-motions. If we now suppose two contiguous particles of different bodies to be affected by different amounts of wave-motion, and that the whole motion be then shared between them, it is clear that one must have gained, and the other lost half the difference; which is the same thing as saying that the amount of heat transferred is as the difference of the temperatures of two bodies. It also appears to me equally clear that if a given amount of heat wavemotion, distributed through a given number of particles, be shared with an equal number previously at rest, each particle of the whole will have halı the wave-motion that previously affected each of the first-mentioned particles : this amounts to the same thing as saying that the temperature is the quotient of the heat in any body divided by the mass.
It therefore appears to me that the matter-theory of heat is not involvedl, as stated by Professor Birks."
but it considers different theories of great antiquity assigned by philosophers, not to man, but to the surface of the earth and its formation. But, even supposing that to be unsound, and suppose the conclusion is that the earth. is not by any means so old as it has been represented to be, and that therefore man, whose remains have been found in it, is not so ancient as has been represented-suppose all that to be established, surely that does not show that there is not still an immense antiquity to fall back upon. Suppose you reduce the past ages of the world's existence from 120,000,000 years to 50,000,000 years, you will still find 50,000,000 years quite enough to deal with. (Laughter.) From the alluvial deposits of the Mississippi the ages assigned by Lyell may have been reduced to not more than 94,000 years ; but though Lyell's first calculation may not be maintained, still a period of 94,000 years would carry the antiquity of man back to a time far more remote than any one has as yet asserted. Suppose, then, that all these statements of the antiquity of the earth are greatly exaggerated and overdrawn, does Professor Birks deny that the Glacial period is removed from the present time by a very large number of years—perhaps hundreds of thousands ? It seems to me to have been indubitably established and maintained by every geologist of repute, that the period during which the earth's surface has existed is sufficient for us to trace a number of years immensely greater tban those periods which we have been accustomed to consider as belonging to the duration of man; and, if that be so, I do not see that we gain anything except a reduction from 250,000,000 to 50,000,000 years ; and even though the strata in which the remains of man are found may have their age reduced to tens or hundreds of thousands of years, instead of to millions, still that gives us an antiquity far beyond anything we bave been accustomed to assign to the existence of man upon the earth. Therefore I do not see that this very elaborate, scientific, and learned paper helps us much with regard to the antiquity of man in relation to the date here assigned to it. We must remember that the paper sets out by determining very absolutely the number of years to which we must limit the existence of man, which we are not permitted to set down at more than 7,000 or 8,000 years. That is laid down as an absolute proposition ; and, more than that, we are told that if we should assume or arrive at a conclusion which places it 10,000 years back, we are not only scientifically wrong, but we have abandoned the very foundation of faith, and we can maintain neither the Bible nor the truths of Christianity. That, I must say, surprised me beyond measure. To be told that if we venture to assume that man has been upon the earth longer than 7,000 or 8,000 years, we are not only wrong, but we contradict the statements of the Bible, and at least implicitly deny the doctrine of the redemption of mankind;-that, I think, is a most dangerous argument. If you lay down certain propositions with regard to facts which are greatly in dispute, or which, at all events, are not generally accepted, and say that any man who differs from you in regard to them is abandoning the doctrines of Christianity, then I say you are using an argument of the most dangerous character, and one of a kind which I think this, above all other societies, is bound to cry out against, and to disown. The principle of this Society is to reconcile science with Christianity, and to find out, as far as we can, how far the truths of Christianity may be harmonized with the discoveries of modern science; and we find a number of scientific men, including nearly all of the greatest eminence, holding the view that man's age upon the earth is considerably longer than 7,000 years. • We must not, even though they may be wrong in their opinions, turn round and tell them that they are infidels, that they are abandoning the principles of Christianity, and that they cannot possibly hold the doctrine of redemption. Our purpose in this Society is, as I have just said, to endeavour to find out how far we can reconcile science and Christianity, and not to place them directly in opposition, as it certainly seems to me that this paper does, from the statements which it makes at its commencement. That is the reason why I cannot help speaking perhaps rather strongly in reference to these propositions. As to the arguments and theories, I am by no means competent to enter upon them, even if I desired to do so; but I do not think they affect the question. But do not let us lay down principles of the kind involved in saying that those who do not agree with you do not hold the doctrines of Christianity. It is the fact that many clergymen do hold views of the kind which Professor Birks condemns, and he seems to condemn them for doing so; but I must say that this is not the manner in which I like to see scientific questions dealt with, holding it out as matter of reproach to any one who dares to hold a contrary opinion. This question of the antiquity of man is an open one, and may be held as an open one by clergymen as well as by other people; and often those clergymen who examine it will find themselves forced to come to conclusions to which Professor Birks is opposed. I am not pretending to discuss this question scientifically, but, like other men, I have read the ordinary works on the subject. Look at this matter historically, look at the monuments to be found in Egypt. Some of those monuments certainly go as far back as the time of Abraham ; and you will find that even those old monuments represent the different races of man as existing at present; the negro with all his peculiar characteristics, and various other peoples also. All these variations arising in the few hundred years that elapsed between the date of the Flood and the time of Abraham; is not this à most striking proof that you must carry your date farther back? (A voice : “No," and laughter.) Well, I do not say that my opinion is to be taken dogmatically. I only state it as it presents itself to my own mind. In maintaining myown views I bring forward strong arguments, as they appear to me, for the great antiquity of man ; I will not say how great, but certainly much greater than those dates which are said to be deduced from the Bible. We must not forget, however, that the Bible has no chronology, that what we accept as the chronology of the Bible was formed by the ingenious calculations of Archbishop Ussher; and we know that many people, quite independent of the scientifio question, hold views of Biblical chronology