[180] I may refer in passing to the researches of A. C. Haddon and Henry Balfour, who have made it seem at least highly probable that all decorative forms originated in the copying of natural objects. [181] F. C. Penrose showed in 1851 that all the quasi-horizontal lines in the Parthenon are really arcs of circles, that the ‘entasis’ or swelling of every pillar is the true arc of an hyperbola, and that there is not a true right-angle nor a strictly vertical column in the building. All good Greek buildings are similarly full of “curves, leaning faces, irregular spacings, and other optical refinements” (Investig. of the Princs. of Athenian Architecture). This principle, called by Ruskin ‘life’ (Seven Lamps) and by some ‘symmetrophobia,’ was most daringly applied in mediæval building. A very striking and well illustrated series of articles on the subject was contributed by Mr. W. H. Goodyear to the _Architectural Record_, Vol. VI, 1896-7. [182] I am indebted in connexion with these remarks on Gothic architecture to a very interesting paper by Mr. L. March Phillipps in the _Contemporary Review_ for September, 1907. [183] For example, when molecules first grouped themselves (supposing that was how it came about) into the form which resulted in living protoplasm, their action was one of a chemico-physical nature, but the response is not expressible in purely chemico-physical terms. Similarly when sensation first appeared in protoplasm. [184] Die Welt als Wille und Vorstellung, Drittes Buch, _Die Platonische Idee das Objekt der Kunst_. [185] Camille Mauclair, French Impressionists. “Light,” writes M. Mauclair, “becomes the sole subject of the picture; the interest of the object upon which it plays is secondary. Painting thus conceived becomes a purely optic art” (p. 32). “The principal person in a picture,” said Manet, “is the light” (p. 42). [186] No one who has seen “Le Penseur,” by Rodin, will doubt that plastic art can render Thought. But literature alone could tell us what he is thinking. INDEX _When a subject is treated on more than one consecutive page, reference is usually made to the first page only._ Action and Reaction, 264 Adaptability, 13, 63 Adaptation, in nature, how regarded by Paley, 3; argument from imperfect adaptations, 4, 14, 136, 143, 152; how conceived by evolution theory, 10, 12; Lamarck’s theory of, 68; Weismann’s theory, 93 _sqq._; Darwin’s explanation, 72; directive theory, 115 _sqq._; effects of new environment, 123 _sqq._ See Co-adaptation Æschylus, 159 _Amblystoma_, 40 (illustration facing), 125 _Amœba_, 30, 47, 143 Amphimixis, 39, 98 _Anabæna_, 141 _Anableps_, 100, 112 Ants, 78, 85, 89, 111, 154 Apperception and Free-will, 172 Arch, effect of, in architecture, 258 Aristotle, 247 _note_