In painting, light effects in connection with colour are of the greatest importance, and are skilfully managed by many masters of the art. Rembrandt may be said to possess the highest genius for their treatment. Without going into particulars of technique, I may note that the pleasure which we derive from light effects in painting may be referred to two opposite extremes. We know that it is out of the question for the painter to transfer to his canvas Nature’s extremes of light and shade, only about half of the eight hundred ascertained degrees of brilliancy being available to him.[114] Helmholtz has shown in an interesting manner how the artist may triumph over this difficulty. It proves to be a special case for the application of Weber’s law; the adjustment of intensities is not in proportion to the actual force of the stimuli, but to their relative force. Thus, when the painter tempers the brilliance of Nature he actually gives a more faithful representation, because the toned-down light against the deepened shadows of a picture produces the same effect on the senses as the clear beams of sunlight in contrast with its luminous shadows.[115] This so-called normal technique is objected to on diametrically opposite grounds. Some painters, refusing to darken and falsify Nature, seek to make their shadows as bright as are those in the diffused light of day. As it is impossible, however, to represent the actual intensity of the light, their attempt to reproduce the actual is only half realized. The true contrast between light and dark fails, and the result is the faded, obscure, hazy appearance which characterizes the work of extremists of this school. In the other direction the attempt is sometimes made to darken the shadows so excessively as actually to make the difference between light and shade greater than it is in Nature. Caravaggio and Ribera, Lenbach and Samberger, furnish examples of this kind of painting. Their work is done on the principle of darkening the shade, in order to bring out the light more sharply; eyes, brow, and hands in their pictures seem to surpass the clearness of Nature because of this difference, which is greater than that of reality. These artists are true lovers of light. (_b_) The Perception of Colour