§ 13. These motives, or motives like them, might perhaps be guessed on looking at the sketch. But no one without going to the spot would understand the meaning of the vertical lines in the left-hand lowest corner. They are a "memorandum" of the artificial verticalness of a low sandstone cliff, which has been cut down there to give space for a bit of garden belonging to a public-house beneath, from which garden a path leads along the ravine to the Lausanne rifle ground. The value of these vertical lines in repeating those of the cathedral is very great; it would be greater still in the completed picture, increasing the sense of looking down from a height, and giving grasp of, and power over, the whole scene. § 14. Throughout the sketch, as in all that Turner made, the observing and combining intellect acts in the same manner. Not a line is lost, nor a moment of time; and though the pencil flies, and the whole thing is literally done as fast as a piece of shorthand writing, it is to the full as purposeful and compressed, so that while there are indeed dashes of the pencil which are unintentional, they are only unintentional as the form of a letter is, in fast writing, not from want of intention, but from the accident of haste. § 15. I know not if the reader can understand,--I myself cannot, though I see it to be demonstrable,--the simultaneous occurrence of idea which produces such a drawing as this: the grasp of the whole, from the laying of the first line, which induces continual modifications of all that is done, out of respect to parts not done yet. No line is ever changed or effaced: no experiment made; but every touch is placed with reference to all that are to succeed, as to all that have gone before; every addition takes its part, as the stones in an arch of a bridge; the last touch locks the arch. Remove that keystone, or remove any other of the stones of the vault, and the whole will fall. § 16. I repeat--the power of mind which accomplishes this, is yet wholly inexplicable to me, as it was when first I defined it in the chapter on imagination associative, in the second volume. But the grandeur of the power impresses me daily more and more; and, in quitting the subject of invention, let me assert finally, in clearest and strongest terms, that no painting is of any true imaginative perfectness at all, unless it has been thus conceived.