And among the first habits that a young architect should learn, is that of thinking in shadow, not looking at a design in its miserable liny skeleton; but conceiving it as it will be when the dawn lights it, and the dusk leaves it; when its stones will be hot and its crannies cool; when the lizards will bask on the one, and the birds build in the other. Let him design with the sense of cold and heat upon him; let him cut out the shadows, as men dig wells in unwatered plains; and lead along the lights, as a founder does his hot metal; let him keep the full command of both, and see that he knows how they fall, and where they fade. His paper lines and proportions are of no value: all that he has to do must be done by spaces of light and darkness; and his business is to see that the one is broad and bold enough not to be swallowed up by twilight, and the other deep enough not to be dried like a shallow pool by a noon-day sun. And that this may be, the first necessity is that the quantities of shade or light, whatever they may be, shall be thrown into masses, either of something like equal weight, or else large masses of the one relieved with small of the other; but masses of one or other kind there must be. No design that is divided at all, and is not divided into masses, can ever be of the smallest value: this great law respecting breadth, precisely the same in architecture and painting, is so important, that the examination of its two principal applications will include most of the conditions of majestic design on which I would at present insist. XIV. Painters are in the habit of speaking loosely of masses of light and shade, meaning thereby any large spaces of either. Nevertheless, it is convenient sometimes to restrict the term "mass" to the portions to which proper form belongs, and to call the field on which such forms are traced, interval. Thus, in foliage with projecting boughs or stems, we have masses of light, with intervals of shade; and, in light skies with dark clouds upon them, masses of shade with intervals of light.