But attention may be more usefully directed to the extravagantly gratuitous guess involved in hypothesis 3. As a minor point, it is not even carefully worded; for entities which cannot be expressed in terms of matter and motion are common enough without going outside the domain of physics. Light, for instance, and Electricity, have not yet proved amenable, and do not appear likely to be amenable, to purely dynamical theory.
Certain phenomena have been reduced to matter and motion,—heat, for instance, and sound, the phenomena of gases and liquids, and all the complexities of astronomy. And in a famous passage Newton expressed an enthusiastic hope that all the phenomena of physics might some day be similarly reduced to the attractive simplicity of the three laws of motion—inertia, acceleration, and stress. And ever since Newton it has been the aim of physics to explain everything in its domain in terms of pure dynamics. The attempt has been only partially successful: the Ether is recalcitrant. But its recalcitrance is not like mere surly obstruction, it is of a helpful and illuminating character, and I shall not be misleading anyone if I cheerfully admit that in some modified and expanded form dynamical theory in mathematical physics has proved itself to be supreme.
But does dominance of that kind give to that splendid science—the glory of Britain and of Cambridge—the right to make a gigantic extrapolation and sprawl over all the rest of the Universe, throwing out tentacles even into regions which it has definitely abstracted from its attention or excluded from its ken? There is not a physicist who thinks so. The only people who try to think so are a few enthusiasts of a more speculative habit of thought, who are annoyed with the physicists, from Lord Kelvin downwards, for not agreeing with them. And being unable to gather from competent authority any specific instance in which dynamics has explained a single fact in the region of either life or mind or consciousness or emotion or purpose or will,—because it is known perfectly well that dynamical jurisdiction does not extend into those regions,—these speculators set up as authorities on their own account, and, on the strength of their own expectation, propound the broad and sweeping dogma that nothing in the Universe exists which is not fully expressible in terms of matter and motion. And then, having accustomed themselves to the sound of some such collocation of words, they call upon humanity to shut its eyes to any facts of common experience which render such an assertion ridiculous.
The energy and enthusiasm of these writers, and the good work they may be doing in their own science, render them more or less immune from attack; but every now and then it is necessary to say clearly that such extravagant generalisations profane the modesty of science: whose heritage it is to recognise the limitations of partial knowledge, and to be always ready to gain fresh experience and learn about the unknown. The new and unfamiliar is the vantage ground, not of scientific dogmatism, but of scientific inquiry.
The expository or theoretical part of this book may at first appear too abstract for the general reader who has had no experience of the kind of facts already described. Such reader may fail to see a connexion between this more didactic portion and the illustrations or examples which have preceded it; but if he will give sufficient time and thought to the subject, the connexion will dawn upon him with considerable vividness.
It has always seemed to the author legitimate, and in every way desirable, for an experimenter to interpret and make himself responsible for an explanation or theory of his observations, so far as he can. To record bare facts and expect a reader of the record to arrive at the same conclusion as that reached by one who has been immersed in them for a long time, is to expect too strenuous an effort, and is not a fair procedure. Such a practice, though not unusual and sometimes even commended in physical science, is not followed by the most famous workers; and it has been known to retard progress for a considerable time by loading the student with an accumulation of undigested facts. The hypothesis on which an observer has been working, or which he has arrived at in the course of his investigations, may or may not be of permanent value, but if his experience has led him to regard it as the best solution so far attainable, and if he is known not to be a specially obstinate or self-opinionated person, his views for what they are worth should be set forth for the guidance of future inquirers. If he mauls the facts in his direction, he will be detected; but such an accusation is a serious one, and should not be made lightly or without opportunity for reply.
The string on which beads are strung may not be extremely durable, and in time it may give place to something stronger, but it is better than a random heap of beads not threaded on anything at all.
The main thread linking all the facts together in the present case is the hypothesis not only of continued or personal psychical existence in the abstract, but a definite inter-locking or inter-communication between two grades of existence,—the two in which we are most immediately interested and about which we can ascertain most,—that of the present and that of the immediate future for each individual; together with the added probabilities that the actual grades of existence are far more than two, and that the forthcoming transition, in which we cannot but be interested even if we do not believe in it, is only one of many of which we shall, in some barely imaginable way, in due time become aware.
The hypothesis of continued existence in another set of conditions, and of possible communication across a boundary, is not a gratuitous one made for the sake of comfort and consolation, or because of a dislike to the idea of extinction; it is a hypothesis which has been gradually forced upon the author—as upon many other persons—by the stringent coercion of definite experience. The foundation of the atomic theory in Chemistry is to him no stronger. The evidence is cumulative, and has broken the back of all legitimate and reasonable scepticism.