The two oil paintings of Petworth Park, still in the Petworth collection, as well as the brilliant unfinished sketch of ‘Petworth Park’ in the National Gallery (No. 559), were probably painted in the house during this visit; at any rate, the sketches in water-colour upon which these canvases were based were made at this time. But when Turner was not busy at his easel or sketching in the park and neighbourhood, he seems to have felt the time hang heavily on his hands, so, to save himself from the ennui of small-talk and idleness, he began making colour sketches, first of the various rooms, then of the furniture and bric-à-brac, and finally of the people staying in the house. These sketches, which number about a hundred, indicate clearly a distinct change in Turner’s outlook upon nature. Up to this time he had invariably employed form as the basis of his work. In these studies we see him turning his attention directly to colour as the chief element [Illustration: _PLATE LXXV_ HONFLEUR BODY COLOUR ON BLUE. ABOUT 1830] [Illustration: _PLATE LXXVI_ COUNTRY TOWN ON STREAM BODY COLOUR ON BLUE. ABOUT 1830] of representation. The difference is no doubt largely a matter of degree, for both elements are indispensable. Yet we have only to compare, say, a drawing like that of ‘Rochester,’ in the _Rivers of England_ series, with any one of the _Rivers of France_ subjects to see that the change of emphasis, upon colour instead of form, was fraught with important technical results. From a psychological point of view the change is also significant. It shows that Turner was dissatisfied with the language of form, which had served him so well all his life; the vague unrest and conflicting emotions which now surged in his bosom demanded a less static, a more fluent and elusive medium of expression.