There are several minor mechanical ways of enhancing relief, most of them providing a setting which acts as a kind of inner frame to the design, the object being to reduce the effect of the actual frame in disturbing the illusion. Portrait painters of the Dutch, Flemish, and English schools, have often placed half length figures in painted ovals on canvas rectangles, and in the case of Hals he sometimes further improved the illusion by extending a hand of the subject over the oval. Hanneman used this oval in a most exceptional way. On a large canvas he painted the bust portraits of Constantine Huygens and his six children, each in a separate oval, the father being in the centre.[a] The scheme is strangely effective, for the attention of the observer is involuntarily confined to one portrait at a time. In genre pictures a doorway may act as the inner frame, but this is only of material value if the picture be of considerable size. The Dutch painters, notably Gerard Dow, loved to paint figures leaning over window-sills, this method usually enhancing the relief, because the eye is apt to be confined for a time to the window-frame. Perhaps the best use of a window for the purpose of relief is Rembrandt's Samson Menacing His Father-in-law, where the old man's head and hands, of life size, are seen protruding from a small window.[b] [a] Hague Gallery. [b] Berlin Gallery. CHAPTER II ILLUSION OF MOTION With human figures--With animals. From the earliest times great sculptors, in producing a single figure in action, have chosen for the representation a moment of rest between two steps in the action, so that the character of these steps is instantly recognized by the observer, whose imagination unconsciously carries through the action. If every part of the figure is built up conformably with the action, with due regard to the position from which the statue is to be seen, an illusion of motion will follow, though this is necessarily so rapid that the effect upon the observer is indirect: he translates the impression into appreciation of the lifelike attitude of the figure. Nearly all the ancient Greek sculptured figures known to us, commencing with those of Myron, are characterized by this excellence in design, and so with the best work of the Italian Renaissance. Modern sculptors of repute have also endeavoured to provide the illusion, Rodin in particular holding that it should be the aim of every sculptor.[69]