Turner, who was not a drawing-master, lay under no necessity to formulate his principles and stick to them. On the contrary, his style developed like a kaleidoscope. He had been in Switzerland and on the Rhine in 1841, "painting his impressions," making water-colour notes from memory of effects that had struck him. From one of these, "Splügen," he had made a finished picture, and now wished to get commissions for more of the same class. Ruskin was greatly interested in this series, because they were not landscapes of the ordinary type, scenes from Nature squeezed into the mould of recognised artistic composition, nor, on the other hand, mere photographic transcripts; but dreams, as it were, of the mountains and sunsets, in which Turner's wealth of detail was suggested, and his knowledge of form expressed, together with the unity which comes of the faithful record of a single impression. The lesson was soon enforced upon Ruskin's mind by example. One day, while taking his student's constitutional, he noticed a tree-stem with ivy upon it, which seemed not ungraceful, and invited a sketch. As he drew he fell into the spirit of its natural arrangement, and soon perceived how much finer it was as a piece of design than any conventional rearrangement would be. Harding had tried to show him how to generalize foliage; but in this example he saw that not generalization was needed to get its beauty, but truth. At Fontainebleau soon after, in much the same circumstances, a study of an aspen-tree, idly begun, but carried out with interest and patience, confirmed the principle. At Geneva, once more in the church where he had formed such resolutions the year before, the desire came over him with renewed force; now not only to be definitely employed, but to be employed in the service of a definite mission, which was, in art, exactly what Carlyle had preached in every other sphere of life in that book of "Heroes": the gospel of sincerity.