§ 9. But farther: these questions of volatility, and visibility, and hue, are all complicated with those of shape. How is a cloud outlined? Granted whatever you choose to ask, concerning its material, or its aspect, its loftiness and luminousness,--how of its limitation? What hews it into a heap, or spins it into a web? Cold is usually shapeless, I suppose, extending over large spaces equally, or with gradual diminution. You cannot have, in the open air, angles, and wedges, and coils, and cliffs of cold. Yet the vapor stops suddenly, sharp and steep as a rock, or thrusts itself across the gates of heaven in likeness of a brazen bar; or braids itself in and out, and across and across, like a tissue of tapestry; or falls into ripples, like sand; or into waving shreds and tongues, as fire. On what anvils and wheels is the vapor pointed, twisted, hammered, whirled, as the potter's clay? By what hands is the incense of the sea built up into domes of marble? And, lastly, all these questions respecting substance, and aspect, and shape, and line, and division, are involved with others as inscrutable, concerning action. The curves in which clouds move are unknown;--nay, the very method of their motion, or apparent motion, how far it is by change of place, how far by appearance in one place and vanishing from another. And these questions about movement lead partly far away into high mathematics, where I cannot follow them, and partly into theories concerning electricity and infinite space, where I suppose at present no one can follow them. What, then, is the use of asking the questions? For my own part, I enjoy the mystery, and perhaps the reader may. I think he ought. He should not be less grateful for summer rain, or see less beauty in the clouds of morning, because they come to prove him with hard questions; to which, perhaps, if we look close at the heavenly scroll,[2] we may find also a syllable or two of answer illuminated here and there. FOOTNOTES: [1] The buoyancy of solid bodies of a given specific gravity, in a given fluid, depends, first on their size, then on their forms. First, on their size; that is to say, on the proportion of the magnitude of the object (irrespective of the distribution of its particles) to the magnitude of the particles of the air.