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Rh carried up far above the crown of the dome, where it is cut off and covered with a small segmental dome surmounted by a tall lantern of stone. The system is devised with a view to stability. The cone shape of the inner drum gives it resistance to the dome thrusts, and these thrusts are further fortified by a solid filling of masonry between the smaller cone above and the vault reaching more than halfway from the springing to the crown. The outer drum is a solid wall up to a level but little higher than the apex of the timber roof of the nave, where it forms a stylobate for the encircling Corinthian order. But the two drums are connected by heavy abutments across the interval between them, one behind each column of the encircling order, with a heavier buttress filling every fourth intercolumniation (Plate XI). The inner drum rises in diminished thickness above the entablature of the outer one in the form of an attic with an order of pilasters and square openings between. From this attic rises a false dome of timber, surrounding and concealing the great cone which is the real support of the lantern.

This remarkable scheme embodies the last notable attempt to solve the great dome problem with which the architects of the Renaissance had struggled from the time of Brunelleschi. But the problem is incapable of a satisfactory solution. It is impossible to make a large unbuttressed dome stand securely except by the extraneous means of binding chains. Wren has not attempted to do such a thing. He was too good an engineer to follow in the footsteps of Brunelleschi and Michael Angelo. His dome is well buttressed, but it is therefore necessarily hidden from view. To raise another dome of masonry from the cornice of the drum for external effect, and to crown such a dome with a stone lantern fifty feet high, he saw to be impossible with safety. A semblance of such a dome was, however, necessary to his scheme. He had been charged to make a dome "conspicuous above the houses," and he therefore surrounded the cone, the true support of the lantern, with a wooden counterfeit of a dome upon which he makes the beholder believe that the lantern rests. The system is thus a monstrous architectural deceit. We have criticised Michael Angelo for springing a great dome from the top of a drum, but he cannot be reproached for deception. His dome is a real dome of masonry, and does carry the lantern as it appears to,