But look at the white clouds carefully, and it will be seen they are not all of the same white; parts of them are quite grey compared with other parts, and they are as full of passages of light and shade as if they were of solid earth. Nevertheless, their most deeply shaded part is that already so much lighter than the blue sky, which has brought us up to our number 30, and all these high lights of white are some 10 degrees above that, or, to white paper, as 40 to 10. And now if you look from the blue sky and white clouds towards the sun, you will find that this cloud white, which is four times as white as white paper, is quite dark and lightless compared with those silver clouds that burn nearer the sun itself, which you cannot gaze upon,--an infinite of brightness. How will you estimate that? And yet to express all this, we have but our poor white paper after all. We must not talk too proudly of our "truths" of art; I am afraid we shall have to let a good deal of black fallacy into it, at the best. Sec. 5. Well, of the sun, and of the silver clouds, we will not talk for the present. But this principal fact we have learned by our experiment with the white paper, that, taken all in all, the calm sky, with such light and shade as are in it, is brighter than the earth; brighter than the whitest thing on earth which has not, at the moment of comparison, heaven's own direct light on it. Which fact it is generally one of the first objects of noble painters to render. I have already marked one part of their aim in doing so, namely, the expression of infinity; but the opposing of heavenly light to earth-darkness is another most important one; and of all ways of rendering a picture generally impressive (see especially Sec. 12. of the chapter just referred to), this is the simplest and surest. Make the sky calm and luminous, and raise against it dark trees, mountains, or towers, or any other substantial and terrestrial thing, in bold outline, and the mind accepts the assertion of this great and solemn truth with thankfulness.