one of these articles which is of an average type, because with this the illusion is more certain, for it is not likely to be disturbed with a mental inquiry into the unusual article. The painter may produce his illusions then without sacrificing anything in his art, and with the surety that good paintings necessarily result in momentary illusions except when form or expression above life experience are dealt with. The first and most important illusion in the art is that of relief, for without this no other illusion can be produced. It is a general condition applying to all work on a flat surface. The other illusions that may be provided are: (a) of opening distance in landscape; (b) of motion in natural actions, as in flowing water; (c) of human and animal actions; (d) of suspension and motion in the air. The two first are dealt with under "Landscape"; the others are now considered. CHAPTER I ILLUSION OF RELIEF The greatest value in the illusion of relief lies in its assistance to recognition, for with the forms rounded by shading and separated with the appearance of relief which they have in nature, details of the work are less likely to complicate the design to the eye, than if the flat surface of the canvas be emphasized by the avoidance of relief. For the eye has to be considered before the mind, and it is of immense importance that the brain should have the least possible work to do in assisting the eye to interpret a thing of art. It would appear then that the minimum extent to which relief should be given in a painting is that point below which the things painted do not seem to have their three dimensions indicated. Beyond this the painter is at liberty to proceed as he pleases. Some great artists, notably Lionardo, were inclined to think that it is impossible to give too much relief to a figure, and this may be so theoretically, but practically there is a line to be drawn because life is limited, and after a certain point is reached, the work of shading for relief is so tedious an operation, that half a lifetime would be required to execute a picture of three or four figures if the artist wished to produce the strongest illusion in his power to give. A Russian artist of high merit who essayed the task, spent an average time of five years in ceaseless toil on each figure he completed, and even then frequently remarked that he had not given to his figures the full relief he desired to exhibit. It is well known that Lionardo gave long and close attention to this matter in his pictures, and he produced some extraordinary examples of relief, of which the finest is, perhaps, the Litta Madonna,[a] but one cannot help regretting that he did not rest satisfied with a lower point of excellence in respect of the illusion, so that he could spend more time in general design. [a] At the Hermitage. See Plate 21.