I call it illusion, although our contact with things may be real, and our sensations and thoughts may be inevitable and honest; because nevertheless it is always an illusion to suppose that our images are the intrinsic qualities of things, or reproduce them exactly. The Ptolemaic system, for instance, was perfectly scientific; it was based on careful and prolonged observation and on just reasoning; but it was modelled on an image--the spherical blue dome of the heavens--proper only to an observer on the earth, and not transferable to a universe which is diffuse, centreless, fluid, and perhaps infinite. When the imagination, for any reason, comes to be peopled with images of the latter sort, the modern, and especially the latest, astronomy becomes more persuasive. For although I suspect that even Einstein is an imperfect relativist, and retains Euclidean space and absolute time at the bottom of his calculation, and recovers them at the end, yet the effort to express the system of nature as it would appear from _any_ station and to _any_ sensorium seems to be eminently enlightening. Theory and practice in the latest science are still allied, otherwise neither of them would prosper as it does; but each has taken a leap in its own direction. The distance between them has become greater than the naked eye can measure, and each of them in itself has become unintelligible. We roll and fly at dizzy speeds, and hear at incredible distances; at the same time we imagine and calculate to incredible depths. The technique of science, like that of industry, has become a thing in itself; the one veils its object, which is nature, as the other defeats its purpose, which is happiness. Science often seems to be less the study of things than the study of science. It is now more scholastic than philosophy ever was. We are invited to conceive organisms within organisms, so minute, so free, and so dynamic, that the heart of matter seems to explode into an endless discharge of fireworks, or a mathematical nightmare realised in a thousand places at once, and become the substance of the world. What is even more remarkable--for the notion of infinite organisation has been familiar to the learned at least since the time of Leibniz--the theatre of science is transformed no less than the actors and the play. The upright walls of space, the steady tread of time, begin to fail us; they bend now so obligingly to our perspectives that we no longer seem to travel through them, but to carry them with us, shooting them out or weaving them about us according to some native fatality, which is left unexplained. We seem to have reverted in some sense from Copernicus to Ptolemy: except that the centre is now occupied, not by the solid earth, but by _any_ geometrical point chosen for the origin of calculation. Time, too, is not measured by the sun or stars, but by _any_ "clock"--that is, by any recurrent rhythm taken as a standard of comparison. It would seem that the existence and