[18] Since the above was written there has certainly been a great change, and the dogmatic confidence in the verity of the scientific "laws" has now (1920) almost disappeared.
[19] Such fictions, however, are (I need not say) quite necessary as our only means of thinking out, however imperfectly, the problems before us (1920).
[20] It is not generally realised how feeble a force gravitation is. It is calculated (Encycl. Brit., Art. Gravitation) that two masses, each weighing 415,000 tons, and placed a mile apart, would exert on each other an attractive force of only one pound. If one, therefore, was as far from the other as the moon is from the earth, their attraction would only amount to 1/57,600,000,000th of a pound. This is a small force to govern the movement of a body weighing 415,000 tons! and it is easy to see that a slight variation in the law of the force might for a long period pass undetected, though in the course of hundreds of centuries it might become of the greatest importance.
[21] As another instance of the same thing, let me quote a passage from Maxwell's Theory of Heat, p. 31; the italics are mine: "In our description of the physical properties of bodies as related to heat we have begun with solid bodies, as those which we can most easily handle, and have gone on to liquids, which we can keep in open vessels, and have now come to gases, which will escape from open vessels, and which are generally invisible. This is the order which is most natural in our first study of these different states. But as soon as we have been made familiar with the most prominent features of these different conditions of matter the most scientific course of study is in the reverse order, beginning with gases, on account of the greater simplicity of their laws, then advancing to liquids, the more complex laws of which are much more imperfectly known, and concluding with the little that has been hitherto discovered about the constitution of solid bodies." That is to say that Science finds it easier to work among gases—which are invisible and which we can know little about—than among solids, which we are familiar with and which we can easily handle! This seems a strange conclusion, but it will be found to represent a common procedure of Science—the truth probably being that the laws of gases are not one whit simpler than the laws of liquids and solids, but that on account of our knowing so much less about gases it is easier for us to feign laws in their case than in the case of solids, and less easy for our errors to be detected.
[22] All our thoughts, theories, "laws," etc., may perhaps be said to touch Nature—as the tangent touches the curve—at a point. They give a direction—and are true—at that point. But make the slightest move, and they all have to be reconstructed. The tangents are infinite in number, but the curve is one. This may not only illustrate the relation of Nature to Science, but also of Art to the materials it uses. The poet radiates thoughts: but he sets no store by them. He knows his thoughts are not true in themselves, but they touch the Truth. His lines are the envelope of the curve which is his poem.
[23] See the report of the joint meeting of the Royal Society and the Royal Astronomical Society, November 6, 1919, when Einstein's theory was discussed.
[24] It is obvious that the Einstein theory, in which Time enters as a kind of fourth dimension in relation to Space, removes us at once out of the whole field of ordinary scientific reasoning and lands us, so to speak, in a new world. The nature of Space (or of the universal medium, whatever it is) in any region—its possible fundamental accelerations there, its "curvature" or non-Euclidean character, and so forth—is supposed, according to this theory, to vary with the amount of matter in, or density of, that region; and the movements of bodies are consequently supposed to take on the characters (accelerations, etc.,) which we ascribe to the action of Gravitation. Gravitation in fact in any region is the manifestation in Time of the attributes of the universal Medium in that region—which latter again is dependent on the degree of Matter present. Thus, Matter, Time, and Space are one phenomenon.
The whole Einstein theory, in fact, is a device to present these three Protean and variable elements of all material existence (Matter, Time and Space) as so far involved and interlaced in each other that they form always an absolute and complete unity. As such the theory is no doubt suggestive, and along the line of future speculation: but it awaits corroboration. If corroborated it will point the way to a new conception of the Universe.
[25] J. S. Mill.