I now turn to the subject of play with colour, as it is practised by adults. In his classification of the arts Kant has, strangely enough, inserted a colour art besides painting, because he looks upon the latter as pre-eminently linear. As a matter of fact, there are several colour arts. Such, to a certain extent, was the glass tinting of the middle ages, which resembles æsthetic tapestry weaving more than it does painting. Pyrotechnics, too, produce very lively enjoyment by means of the play of light and colour, and finally we have that modern invention, the serpentine dance, which seems to be quite near to music in the direction of sensuous gratification, while far below it as a means of intellectual expression. Those modern painters who strive only to impart colour-tone and harmony, to make the effect of their pictures resemble that of music, are far surpassed by the serpentine dance (a fact which is sufficient to prove that such an aim is mistaken). Here is actual rhythmical movement, ecstasy terminating in itself, waving and attenuation as of tone, and, above all, the thing that moves us so, the succession of glowing colours on a dark background, whose intensity takes hold of the beholder’s soul as only the noblest of musical instruments or perfectly harmonious voices can. (_c_) Perception of Form Recognition, the first requirement for reproduction, is dependent on perception of form. Later, in considering mental experimentation, I shall return to this subject and treat it more fully. Here I will make only the general statement that the visible form of objects is of higher biological value to the exceedingly important faculty of recognition than is colour or brilliancy. Evidently the child has a very special interest in form, or he could not without great effort distinguish the meaning of simple outline at the relatively early age when we find him doing so. It is remarkable how indifferent little children are to gay colour in pictures. Konrad Lange has treated the subject exhaustively in his well-known book, and Sigismund says: “I can not affirm that there is any preference for coloured pictures at this age (two years). When I laid before the child copies of the same picture done in colours and in black and white he seemed to regard them with equal pleasure.”[130] This indifference is displayed, too, by children who take the liveliest interest in a gaudy ribbon or bright flowers; therefore it seems to me probable that the child is so concentrated in the apperception of form that he has no attention left to bestow on the colour—a legitimate argument for the importance of form in recognition. Very striking, too, is the child’s extraordinary capacity for illusion in the observation of form. When Souriau says, “Regarder un dessin, c’est voir des chimères dans les nuages,” he rightly adds that it applies with special force to children.[131] “Mere outlines,” says Sigismund, “serve for any object of that general shape.