But there is a greater surprise in the case of the famous dome. It is generally assumed that what is seen inside the church is but the inner surface of the outer dome. But in nearly every constructed dome there is an inner shell, with a space between it and the outer dome. The reason is, it would be impossible to raise so ponderous a piece of vaulting in the air. Only a construction of a small and shallow kind could be thus supported, and a light outside shell of timber and lead is framed over it. But few could suppose what a tremendous disproportion exists between the outer and innermost shells of St. Paul’s dome, the latter being some fifty feet below the other! The daring plans of Wren made him adopt no less than _three_ casings for this dome. His object was to surmount all by a massive stone lantern, to be capped by the gilt ball and cross; but the difficulty was that the weight would be so great that no system of arching would support it. He therefore carried up from the base whence the dome springs an enormous funnel-shaped cone of brick, on which he securely built his stone lantern, the sides of the funnel being perfectly straight. This erection, which is so lofty that it would hardly stand under the roof of the nave, is, in parts, only a couple of bricks thick, yet it supports a massive structure in the air; and to prevent its spreading at the base, the ingenious architect wound round it a vast chain, which he sunk in molten lead. Outside the funnel was placed the grand dome, which is simply a wooden shell covered with lead, while, to hide the funnel within, a second dome was constructed below. This is the one that exhibits the Thornhill paintings. A grand dome is like an epic for the architect, and the story of the dome of St. Peter’s is a romance; but when we think of an architect carrying up with him to the clouds, that is, to the height of 360 feet from the ground, a stone temple 40 or 50 feet high, to be there perched securely, defiant of storms, the head grows dizzy. Nor does this exhaust the singularities of the structure. The line of the circular wall that is behind the visitor to the Whispering Gallery slopes inwards at a sharp angle, and continues to do so all the way upwards. “I think,” says Hawthorne, “I must have been under a spell of enchantment to-day, connecting me with St. Paul’s; for, trying to get away from it by various avenues, I still got bewildered, and again and again saw its great dome and pinnacles before me. It is very beautiful, very rich. I did not think that anything but Gothic architecture could have so interested me. The statues, the niches, the embroidery as it were of sculpture traced around it, produced a delightful effect.