To show my general meaning, and why I consider the claim an impossible one, let us imagine a little cell—one of the myriads which constitute the human body—professing in the same sort of way to stand outside the body and explain the laws of the other cells and the body at large. It is obvious that the little cell, swept along in the currents of the body and swayed by its emotions, in close proximity and contact with some portions of the organism, and far remote from others, cannot possibly pretend to any such impartial judgment. It is obvious not only that it would not have all the clues of the problem at its command, but that its own needs and experiences would prejudice it frightfully in the interpretation of such clues as it had. Yet man is such a little cell in the body of Nature, or, if you like, in the body of the Society of which he forms a part.
There is, however, one way, it seems to me, in which a cell in the human body might come to an adequate understanding of the body; and that would be rather through experience than through direct reasoning. It is conceivable that there might be some cell in the body which, through the nerves, etc., was in actual touch and sympathetic relationship with every other cell. Then it certainly would have the materials of the required solution. Every change in other parts of the body would register itself in this particular cell; and its little brain (if it had one), without exactly making any great effort, would reflect sympathetically the structure of the whole body—would become, in fact, a mirror of it. This will perhaps give you the key to my notion of what a true Science might be.
But before proceeding to that, I want to go a little more in detail into the fallacy of the absolute intellectual view of Science. I say, first, that a complete summary of any object or process in Nature is impossible; secondly, that such summary as we do make is, and must inevitably and necessarily be, coloured by the underlying feeling with which we approach that phase of Nature.
To take the first point. You say, Why is a complete summary not possible? A watch or other machine may be completely described and defined; why should not (with a little more knowledge) a fir-tree, or the human eye, or the solar system, be completely described and defined?
And this brings us to what may be called the Machine-view of Science. It is curious (and yet I think it will presently be seen that it is quite what might have been expected) that during this century or so, in which Machinery has played such an important part in our daily and social life, mechanical ideas have come to colour all our conceptions of Science and the Universe. Modern Science holds it as a kind of ideal (even though finding it at times difficult to realise) to reduce everything to mechanical action, and to show each process of Nature intelligible in the same sense as a Machine is intelligible. Yet this conception, this ideal, involves a complete fallacy. For the moment you come to think of it, you see that no part of Nature really even resembles a machine.
What is a machine in the ordinary sense? It is an aggregation of parts put together to fulfil certain definite actions and no others. A sewing-machine fulfils the purpose of sewing, a watch fulfils that of keeping time, and they fulfil those purposes only. All their parts subserve those actions, and in that sense may be completely described—as far as just their mechanical action is concerned—the same by a thousand mechanicians. But I make bold to say that no object in Nature fulfils just one action, or series of actions, and no others. On the contrary, every object fulfils an endless series of actions.
Let us take the Human Eye. And I choose this as an instance most adverse to my position, for there is no doubt that the Human Eye is one of the most highly specialised objects in creation. Helmholtz, as you know, is said to have remarked concerning it that if an Optician had sent him an instrument so defective he should have returned it with his compliments. Helmholtz was a great man, and I will not do him the injustice to suppose that he did not know what he was saying. He knew that, regarded as a machine for focussing rays of light, the eye was decidedly defective; but then he knew well enough, doubtless, why it was defective—namely, because it is by no means merely such a machine, but a great deal more.
The Eye, in fact, not only fulfils the action of focussing rays of light—like an Opera Glass or a Telescope—but it might be compared to another instrument, a Photographic Camera, in respect of the fact that it forms a picture of the outer world which it throws on a sensitive plate at the back—the Retina. But then, again, it is unlike any of these "machines," in the fact that it was never made by any Optician, human or divine, for any one definite purpose. On the contrary, as we know, it has grown, it has evolved; it has come down to us over the centuries, and over thousands and thousands of centuries, from dim beginnings in the lowliest organisms who first conceived the faculty of Sight, continually modified, continually shapen by small increments in various directions, in accordance with the myriad needs of a myriad creatures, living, some of them in water, some of them in air, requiring some of them to see at close quarters, some at great distances, some by one kind of light, some by another, and so forth. So that to-day it not only contains a great range of inherited, yet latent, faculties, but it is actually, in its complex structure, an epitome and partial record of its own extraordinary history.
As an instance of this last point, let me remind you that Sight was originally a differentiation of Touch. The light, the shadows, falling on the sensitive general surface of a primitive organism provoke a tactile irritation. In the course of evolution this sense specialises itself at some point of the surface into what we call Sight. Now, to-day, when the little picture formed by the fore-part of the Human Eye falls upon the Retina at the back, it falls upon a screen formed by the myriad congregated finger-tips, so to speak, of the optic nerve—the rods and cones, so-called—which cover like a mosaic the whole ground of the Retina, and feel with their sensitive points the images of the objects in the outer world. And so Sight is still Touch—it is the power of feeling or touching at a distance—as one sometimes in fact becomes aware in looking at things.
But then again on and beyond all these things—beyond the focussing and photographing of rays, beyond the latent adaptations to the needs of innumerable creatures, and the epitomising of ages of evolution—the Human Eye has faculties even more far-reaching perhaps and wonderful. It is the marvellous organ of human Expression. By the dilatations and contractions of the iris, by the altering convexities of the lens and the eyeball, and in a hundred other ways, it manages somehow to convey intelligence of Command, Control, Power, of Pity, Love, Sympathy, and all those myriad emotions which flit through the human mind—an endless series—a perfect encyclopædia. It is difficult even to imagine the eye without this power of language. And what other functions it may have it is not necessary to inquire. Highly specialised though it is, it is already obvious enough that to call it a Machine for focussing rays of light is monstrously and ludicrously inadequate—even as it would be to call the Heart (the very centre of emotion and life, and the symbol of human love and courage) a common Pump.