It is probable that these slight differences between the engraving and the water-colour were made involuntarily, for it is evident that Turner did not have the engraving under his eyes while he was making the drawing. He had probably seen the engraving in some shop-window, and had made a hasty pencil sketch of the part that interested him. That he was working from a somewhat perfunctory sketch and not direct from the original is proved by the fact that he has introduced three arches into the building on the quay immediately at the foot of the tower, instead of the two in Sandby’s engraving. But in the engraving there is a small rounded turret on the battlements of the quay which comes just in front of the place where Turner has introduced his third arch. It is clear that he mistook the indication of this turret in his rough sketch for a third arch in the building beyond. It would, of course, be imprudent to suppose that Turner chose to work in this way partly from memory, with the deliberate intention of giving his imagination freer play; he was probably forced to do so by the material exigencies of his position. But certainly this way of working was admirably calculated to strengthen his memory and call into play his innate powers of arrangement and adaptation. The colour scheme, which is probably the artist’s own invention, is light and pleasing. The golden rays of the setting (? rising) sun are painted with evident enjoyment. The warm yellow light of the sun is transfused over the whole of the sky, turning the distant clouds into crimson. The keynote of the colour is thus orange yellow, passing through pink to burnt sienna. In spite of the lightness of the colour the drawing was worked over a black and white foundation, light washes of Indian ink having been used to establish the broad divisions of light and shade in the design. These washes afterwards formed the ground-work of the greys and cooler colours, being warmed in parts (as in the tower) with washes or touches of pink and burnt sienna, or worked up into more positive hues by subsequent washes of blue and yellow. The handling of the drawing--the sharp decided touches, the neatness and dexterity of its washes, and the rapid march of the whole work--shows what a hold the idea of a unified work of art had already obtained over Turner’s mind. The clear, determined workmanship shows that he must have been thinking of the whole from the beginning, and not of the representation of a number of separate natural objects.