The floor of the choir, and indeed of the whole church, is paved with marble: but within the rails of the altar with porphyry, polished and laid in several geometrical figures.

But to be more particular: as the disposition of the vaultings within is an essential beauty, without which many other ornaments would lose their effect, so the architect was particularly careful in this respect. “The Romans,” says the author of the Parentalia, “used hemispherical vaultings, and Sir Christopher chose those as being demonstrably lighter than the diagonal cross vaults: so the whole vault of St. Paul’s consists of twenty-four cupolas cut off semicircular, with segments to join to the great arches one way, and which are cut across the other, with eliptical cylinders to let in the upper lights of the nave; but in the isles the lesser cupolas are both ways cut in semicircular sections, and altogether make a graceful geometrical form, distinguished with circular wreaths which is the horizontal section of the cupola; for the hemisphere may be cut all manner of ways into circular sections; and the arches and wreaths being of stone carved, the spandrels between are of sound brick, invested with stucco of cockle-shell lime, which becomes as hard as Portland stone; and which having large planes between the stone ribs, are capable of the farther ornaments of painting, if required.

“Besides these twenty-four cupolas, there is a half cupola at the east, and the great cupola of 108 feet in diameter at the middle of the crossing of the great isles. In this the architect imitated the Pantheon at Rome, excepting that the upper order is there only umbratile, and distinguished by different coloured marbles; in St. Paul’s it is extant out of the wall. The Pantheon is no higher within than its diameter; St. Peter’s is two diameters; this shews too high, the other too low; St. Paul’s is a mean proportion between both, which shews its concave every way, and is very lightsome by the windows of the upper order, which strike down the light thro’ the great colonade that encircles the dome without, and serves for the abutment of the dome, which is brick of two bricks thick; but as it rises every way five feet high, has a course of excellent brick of eighteen inches long banding thro’ the whole thickness; and moreover, to make it still more secure, it is surrounded with a vast chain of iron strongly linked together at every ten feet. This chain is let into a channel cut into the bandage of Portland stone, and defended from the weather by filling the groove with lead.

“The concave was turned upon a center; which was judged necessary to keep the work even and true, though a cupola might be built without a center; but it is observable that the center was laid without any standards from below to support; and as it was both centering and scaffolding, it remained for the use of the painter. Every story of this scaffolding being circular, and the ends of all the ledgers meeting as so many rings, and truly wrought, it supported itself. This machine was an original of the kind, and will be an useful project for the like work, to an architect hereafter.

“It was necessary to give a greater height than the cupola would gracefully allow within, tho’ it is considerably above the roof of the church; yet the old church having before had a very lofty spire of timber and lead, the world expected that the new work should not, in this respect, fall short of the old; the architect was therefore obliged to comply with the humour of the age, and to raise another structure over the first cupola; and this was a cone of brick, so built as to support a stone lanthorn of an elegant figure, and ending in ornaments of copper gilt.

“As the whole church above the vaulting is covered with a substantial oaken roof, and lead, the most durable covering in our climate, so he covered and hid out of sight the brick cone, with another cupola of timber and lead; and between this and the cone, are easy stairs that ascend to the lanthorn. Here the spectator may have a view of such amazing contrivances as are indeed astonishing. He forbore to make little luthern windows in the leaden cupola, as are done out of St. Peter’s, because he had otherwise provided for light enough to the stairs from the lanthorn above, and round the pedestal of the same, which are now seen below; so that he only ribbed the outward cupola, which he thought less Gothic than to stick it full of such little lights in three stories one above another, as is the cupola of St. Peter’s, which could not without difficulty be mended, and, if neglected, would soon damage the timbers.”

As Sir Christopher was sensible, that paintings, tho’ ever so excellent, are liable to decay, he intended to have beautified the inside of the cupola with mosaic work, which strikes the eye of the beholder with amazing lustre, and without the least decay of colours, is as durable as the building itself; but in this he was unhappily over-ruled, tho’ he had undertaken to procure four of the most eminent artists in that profession from Italy; this part is however richly decorated and painted by Sir James Thornhill, who has represented the principal passages of St. Paul’s life in eight compartments, viz. his conversion; his punishing Elymas, the sorcerer, with blindness; his preaching at Athens; his curing the poor cripple at Lystra, and the reverence paid him there by the priests of Jupiter as a God; his conversion of the jailer; his preaching at Ephesus, and the burning of the magic books in consequence of the miracles he wrought there; his trial before Agrippa; his shipwreck on the island of Melita, or Malta, with the miracle of the viper. These paintings are all seen to advantage by means of a circular opening, through which the light is transmitted with admirable effect from the lanthorn above.

The highest or last stone on the top of the lanthorn, was laid by Mr. Christopher Wren, the son of this great architect, in the year 1710; and thus was this noble fabric, lofty enough to be discerned at sea eastward, and at Windsor to the west, begun and compleated in the space of thirty-five years, by one architect, the great Sir Christopher Wren; one principal mason, Mr. Strong; and under one Bishop of London, Dr. Henry Compton: whereas St. Peter’s at Rome, the only structure that can come in competition with it, continued an hundred and fifty five years in building, under twelve successive architects; assisted by the police and interests of the Roman see; attended by the best artists of the world in sculpture, statuary, painting and mosaic work; and facilitated by the ready acquisition of marble from the neighbouring quarries of Tivoli.

The curiosities in this cathedral which strangers pay for seeing. On entering the south door, there is a pair of stairs within a small door on the right, leading to the cupola, and the stranger by paying two pence may gratify his curiosity with a prospect from the iron gallery at the foot of the lanthorn, which in a clear day affords a fine view of the river, of this whole metropolis and all the adjacent country, interspersed with pleasant villages.

The ascent to this gallery is by 534 steps, 260 of which are so easy that a child may without difficulty ascend them; but those above are unpleasant, and in some places very dark; but the little light that is afforded is sufficient to shew amazing proofs of the wonderful contrivances of the architect. But as the first gallery, surrounded by a stone balustrade, affords a very fine prospect, many are satisfied, and unwilling to undergo the fatigue of mounting higher.