Now, in translating sketches made with the pencil point into engraving, we must either engrave delicately and expensively, or be content to substitute for the soft varied pencil lines the finer and uncloudlike touches of the pen. It is best to do this boldly, if at all, and without the least aim at fineness of effect, to lay down a vigorous black line as the limit of the cloud form or action. The more subtle a painter's finished work, the more fearless he is in using the vigorous black line when he is making memoranda, of treating his subject conventionally. At the top of page 224, Vol. IV., the reader may see the kind of outline which Titian uses for clouds in his pen work. Usually he is even bolder and coarser. And in the rude woodcuts I am going to employ here, I believe the reader will find ultimately that, with whatever ill success used by me, the means of expression are the fullest and most convenient that can be adopted, short of finished engraving, while there are some conditions of cloud-action which I satisfy myself better in expressing by these coarse lines than in any other way. [2] If the figures are supposed to include less than one-fourth of the horizon, the shaded figures represent diamond-shaped clouds; but the reader cannot understand this without studying perspective laws accurately. [3] In reality, the retiring ranks of cloud, if long enough, would, of course, go on converging to the horizon. I do not continue them, because the figures would become too compressed. [4] I use ellipses in order to make these figures easily intelligible; the curves actually _are_ variable curves, of the nature of the cycloid, or other curves of continuous motion; probably produced by a current moving in some such direction as that indicated by the dotted line in Fig. 3, Plate 56. [5] Now in the possession of E. Bicknell, Esq., who kindly lent me the picture, that I might make this drawing from it carefully. [6] I cannot yet engrave these; but the little study of a single rank of cirrus, the lowest in Plate 63, may serve to show the value of perspective in expressing buoyancy. It is not, however, though beautifully engraved by Mr. Armytage, as delicate as it should be, in the finer threads which indicate increasing distance at the extremity. Compare the rising of the lines of curve at the edges of this mass, with the similar action on a larger scale, of Turner's cloud, opposite. [7] In the autobiography of John Newton there is an interesting account of the deception of a whole ship's company by cloud, taking the aspect and outline of mountainous land. They ate the last provision in the ship, so sure were they of its being land, and were nearly starved to death in consequence. CHAPTER III. THE CLOUD-CHARIOTS.