About half of the present volume appeared in _The Independent_ of November 29, December 7, 13, and 20, 1919, and I am indebted to Hamilton Holt, the editor, and to Karl V. S. Howland, the publisher of that magazine, for the privilege of reprinting them in book form. I am further grateful to several professors of physics, mathematics, astronomy and philosophy who have been kind enough to criticize and correct this material, but since it would not be fair to hold them responsible for my personal views and unconventional language I shall have to express my thanks to them in private. INDEX Bergson, Henri, 47, 51, 52 Carlyle, iv Curvature of space, 26, 35, 38, 96 Eclipse observations, 2, 65, 72 Einstein, Albert Postulates of, 13, 83, 111 Theory of time, 109 Theory of gravitation, 39, 58, 76, 80, 86, 93, 96, 109 Life of, 78 Works of, 116, 117 Equivalence, principle of, 14, 83, 86 Ether, 8, 11, 88, 106 Flammarion, Camille, 40 Flatland, 35, 57 Fourth dimension, 24, 34, 49 Gravitation, 68, 74, 77, 80, 86, 90 Laws, natural, 102, 109 Light, deflection of ray, 11, 62, 79, 85 Light, pressure of, 67, 93 Lodge, Sir Oliver, 2, 68, 75, 87, 88 Lorentz, 22, 111, 112, 118 Macdonald, George, 34 Maxwell, Clerk, 67, 111, 112 Mercury, orbit of, 14, 66 Michelson and Morley experiment, 11, 21, 22, 85 Minkowski, iv, 18 Mirror, images, 18 Motion picture illustrations, 31, 44, 46, 50, 53 Newton, 15, 23, 39, 66, 76, 79, 87, 90, 95 Non-Euclidean geometry, 30, 48, 57, 112 Planck, 98, 121 Poincaré, H., 88, 107 Relativity of measurements, 15, 20, 26 Relativity of motion, 4, 8, 15, 23 Relativity of time, 15, 24, 47, 51 Slade, 58, 60 Spectrum, shifting of lines of, 14, 77, 85 Theories, reception of new, 98, 101 Theory of relativity, 2, 15 Thomson, Sir Joseph, 3, 93, 94, 95 Time as fourth dimension, 30, 32, 49 Time, reversal of, 41, 44 Wells, H. G., 32, 34, 40, 52 Zöllner, 58, 60 =TRANSCRIBER’S NOTES= Simple typographical errors have been silently corrected; unbalanced quotation marks were remedied when the change was obvious, and otherwise left unbalanced. Punctuation and spelling were made consistent when a predominant preference was found in the original book; otherwise they were not changed. Inconsistent hyphens left as printed.