CHAPTER XXXIV.

THE DISCOVERY OF PAST AND FUTURE EVENTS IN GENERAL.

WHEN we wish to ascertain some specific fact that we have not been able to observe for ourselves there are only two ways of doing it. One is to depend upon the testimony of others; and the other is to draw an inference from what we know of the general laws of nature and the specific facts that we or others have observed. The latter method can be described very briefly, and so we shall speak of it first. This is the method used in tracing the history of the solar system from, or rather back to, the vapor and the star-dust from which the planets were made and in prophesying the condition of cold and darkness and lifelessness to which they may be destined. It is the method pursued by geology in tracing the changes which have taken place on the earth's crust and prophesying those which will take place. And it is the method pursued by evolutionary biology in tracing the history of life in the world as it has developed from one form to another. In all these sciences the starting-point is the present, and the question is always this: Granting the truth of the general laws assumed or ascertained by various sciences, what is the only concrete state of affairs that could have preceded the one which we observe to exist at the present, and what is the only concrete state of affairs that can succeed it?

The first thing to notice about this method is that we

always start from the present. In telling about history of any sort we may often begin at the beginning'. The startIn investigating it we never can. Moreover, if ing-point. we are mistaken about some of the general laws or if we are not quite accurate about some of the concrete facts with which we start, the consequences of our error will affect all our history and all our prophecy; and since there is a chance of overlooking some essential fact or making some miscalculation at each stage of our regress into the past or progress into the future, the chances are that the farther we go the less accurate our account of things can be. The possibility of such accumulation of errors will always make a definite and detailed description of the world more doubtful the farther the described state of affairs is removed from the present data with which we have to start. But indeed what we know about the laws of nature and present concrete conditions is so slight in comparison with what we do not know, and even those things that we do know are so enormously complex, that no one really attempts to work out the problem in all its details, and the most that any scientist attempts to tell about either the distant past or the distant future is the broad outlines of things, which would remain substantially the same no matter what were true about any one of countless smaller details. A geologist can tell with perfect confidence that where there is now a certain group of hills there was once a fairly level plateau, and he can tell that the change from one to the other was due in the main to the action of water running down to the valley below, but he would never attempt to tell the exact location of every stream or the amount of earth that one of them carried down on some particular day ten thousand years ago.

Even what a geologist does tell about the past and the future is not based upon the most ultimate laws of matter known. If it were, he would have deduced the history of the world from the known laws of chemistry and molecular physics; and such deduction is impossible because the situ

ations that these sciences deal with are exceedingly simple, and from the relations that are found to exist in these simple situations no one could possibly calculate what would happen under the vastly more complex conditions that are dealt with in geology. The geologist starts rather with empirical laws which are much less precise (so far as particular molecules are concerned) than the laws of molecular physics, but which give a much better idea of what happens when things are arranged as he supposes them to be in the large. He sees, for example, that streams actually do wear away earth and rock from their beds and carry the débris away, and he determines by actual measurement the amount of earth of a given kind that a stream of a given size and swiftness carries off in a given length of time; and then he applies the 'empirical law' which he derives from such measurements directly to the problem in hand. He knows, of course, that the facts in the case are consistent with molecular physics, but he knows also that his data are much too crude and complex to be dealt with by that science; and so he works away with his empirical laws' in comparative oblivion of it. Almost all of our history of the world and our prophecy of its future is based upon such empirical laws' as these, derived from a view of things in the large; and of course any history or prophecy which is based altogether upon such broad rough laws cannot attempt to describe small details. Another thing to notice about scientific history and prophecy is that there is nothing in the laws and concrete facts upon which they are based to tell the scientist The limit. when the whole world-process began or when it will come to an end. For all we know or ever could know, God may annihilate the whole world to-morrow; but our prophecy based on laws and concrete facts of the present looks forward without limit towards a whole eternity. In the same way we trace what we suppose to be the broad outlines of history further and further into the past, and we never reach and never can reach a point at which we can say: Here everything

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must have begun. If the world ever was made and wound up like a watch, whether five thousand years ago, as theologians used to suppose, or twenty-four hours ago, we can never see anything on the face of it to indicate when that took place. All we can say is that if this world-watch really was going six thousand years ago as it is going now, then at precisely that time the hands were in such and such a position.

It seems much easier to believe that the world started five thousand or five billion years ago than twenty-four hours ago, merely because our whole conception of so distant a past ïs vaguer. But if it started five thousand years ago, it started with fossils in the rocks and all the other absolutely definite conditions that must have preceded the present and that lead scientists to trace its history beyond the five thousand years of its actual existence. And if it started five billion years ago, every detail must have been just as definite; however hazy our idea of it may be. It might just as well have been created twenty-four hours ago with mines half empty and cities all built and ships in the harbors, and adult human beings busy at their work, with brains so fashioned that they look back towards an imaginary past and believe they remember it. Thus, starting from the present as science does and must, and assuming as it does that things acted in the past and will act in the future according to the same laws that we find now, it is quite impossible for us to find any point at which the world-process must have begun or must come to an end, even if there really was such a beginning and really will be such an end.

• Monu-
ments.'

One might think that the uncertainty due to the fragmentary nature of our knowledge and this possible accumulation of errors should affect our knowledge of the past quite as much as our knowledge of the future; but as a matter of fact it does not. We know a great deal more about the past; and the reason is that many conditions, when they are once produced, remain practically unaltered for a great many years. No geologist can tell whether the

place where I am now writing will ever be covered with water or not; but from the layer of gravel beneath the surface of the ground I can infer with reasonable certainty that once it was. No one can tell whether Vesuvius will ever destroy a city again, but from the buried remains of Pompeii and from written records we can infer that once it did. This

is merely because we have reason to believe that such things as beds of gravel, the stones of buried cities and forgotten documents remain comparatively unchanged for years or centuries. Thus when we find such things they take us at one leap beyond all the intervening years, and each of them shows us one fragment of the past as it existed at the time.

Accordingly, if we are right in assuming that such relics of the past have remained unaltered in any given respect, and if we have any means of finding out their age, we can use each one of them as a starting-point in the construction of the past, or at least as something fixed by which to test our inferences about it. In such cases we might almost say that we really do start with the past. This is why we can tell more about some things in the past than in the future; why there is such a thing as serious history where there is no corresponding prophecy.

It is because there are such absolutely or relatively permanent monuments' of the past as these that it is possible for us to distinguish between relatively direct evidence concerning past events and indirect. The most direct evidence concerning any event is, of course, the present and personal perception of the event itself. This is something independent of 'monuments' of any sort, but if the event is past, this evidence is unattainable. The most direct evidence then possible is the perception of something which we can assume to be a direct effect of the event, and after that the supposed effects of effects of the event or the supposed effects of something that would have caused the event; until the chain is as long or crooked as you please. The most direct evidence of the destruction of Pompeii by a volcanic eruption would be