And the beauty--(observe this carefully)--the beauty of Gothic arches, and of their foliation, always involves reference to the strength of their structure; but only to their structure as _self-sustaining; not as sustaining superincumbent weight_. In the most literal of senses, "the earth hath bubbles as the water hath; and these are of them." 138. What do you think made Michael Angelo look back to the dome of Santa Maria del Fiore, saying, "Like thee I will not build one, better than thee I cannot"? To you or to me there is nothing in that dome different from hundreds of others. Which of you, who have been at Florence, can tell me honestly he saw anything wonderful in it? But Michael Angelo knew the exact proportion of thickness to weight and curvature which enabled it to stand as securely as a mountain of adamant, though it was only a film of clay, as frail, in proportion to its bulk, as a sea shell. Over the massy war towers of the city it floated; fragile, yet without fear. "Better than thee I cannot." 139. Then think what the investigation of the bottle branches into, joined with that of its necessary companion, the cup. There is a sketch for you of the cup of cups, the pure Greek κάνθαρος, which is always in the hand of Dionusos, as the thunderbolt is in that of Zeus. Learn but to draw that thoroughly, and you won't have much more to learn of abstract form; for the investigation of the kinds of line that limit this will lead you into all the practical geometry of nature; the ellipses of her sea-bays in perspective; the parabolas of her waterfalls and fountains in profile; the catenary curves of their falling festoons in front; the infinite variety of accelerated or retarded curvature in every condition of mountain debris. But do you think mere science can measure for you any of these things? That book on the table is one of the four volumes of Sir William Hamilton's "Greek Vases." He has measured every important vase vertically and horizontally, with precision altogether admirable, and which may, I hope, induce you to have patience with me in the much less complex, though even more scrupulous, measurements which I shall require on my own examples. Yet English pottery remains precisely where it was, in spite of all this investigation. Do you fancy a Greek workman ever made a vase by measurement? He dashed it from his hand on the wheel, and it was beautiful: and a Venetian glass-blower swept you a curve of crystal from the end of his pipe; and Reynolds or Tintoret swept you a curve of colour from their pencils, as a musician the cadence of a note, unerring, and to be measured, if you please, afterwards, with the exactitude of Divine law.