In proceeding to consider this subject, we assume that the painter is generally acquainted with our sketch of the theory of colours, and that he has made himself well acquainted with certain chapters and rubrics which especially concern him. He will thus be enabled to make use of theory as well as practice in recognising the principles of effect in nature, and in employing the means of art. COLOUR IN GENERAL NATURE. 872. The first indication of colour announces itself in nature together with the gradations of aërial perspective; for aërial perspective is intimately connected with the doctrine of semi-transparent mediums. We see the sky, distant objects and even comparatively near shadows, blue. At the same moment, the illuminating and illuminated objects appear yellow, gradually deepening to red. In many cases the physiological suggestion of contrasts comes into the account, and an entirely colourless landscape, by means of these assisting and counteracting tendencies, appears to our eyes completely coloured. 873. Local colours are composed of the general elementary colours; but these are determined or specified according to the properties of substances and surfaces on which they appear: this specification is infinite. 874. Thus, there is at once a great difference between silk and wool similarly dyed. Every kind of preparation and texture produces corresponding modifications. Roughness, smoothness, polish, all are to be considered. 875. It is therefore one of the pernicious prejudices of art that the skilful painter must never attend to the material of draperies, but always represent, as it were, only abstract folds. Is not all characteristic variety thus done away with, and is the portrait of Leo X. less excellent because velvet, satin, and moreen, are imitated in their relative effect? 876. In the productions of nature, colours appear more or less modified, specified, even individualised: this may be readily observed in minerals and plants, in the feathers of birds and the skins of beasts. 877. The chief art of the painter is always to imitate the actual appearance of the definite hue, doing away with the recollection of the elementary ingredients of colour. This difficulty is in no instance greater than in the imitation of the surface of the human figure. 878. The colour of flesh, as a whole, belongs to the active side, yet the bluish of the passive side mingles with it. The colour is altogether removed from the elementary state and neutralised by organisation. 879. To bring the colouring of general nature into harmony with the colouring of a given object, will perhaps be more attainable for the judicious artist after the consideration of what has been pointed out in the foregoing theory. For the most fancifully beautiful and varied appearances may still be made true to the principles of nature. CHARACTERISTIC COLOURING. 880.