Comparing the cupolas of St. Peter's and St. Paul's, we shall find that, though the latter has, in a great degree. been the model of the former, there is a material difference in the decorative part. though the general idea of the construction is the same. In St.. Peter's the buttresses of the dome tower, though decorated each with two engaged columns and pilasters projecting from the cylindric wall, destroy the con tinuity, and render the e&ct disagreeable. The dome is like wise pierced with three ranges of little dormer-windows, which are suffered to spot and break the surface for the pal try consideration of lighting the interior staircases. The idea, originated in St. Paul's, lies been prosecuted in the church of St. Genevieve at Paris, where the appearance of a peripteral temple is completely obtained, as the columns surrounding the tambour are all insulated ; but, it is to be lamented, that the dome itself should be so deficient in grandeur of dimen sions, and grace of proportions, as to destroy the effect of this beautiful decoration.
Beginning the examination of the interior of St. Paul's at the west end, we find the body of the building, as to the general form, entirely upon the plan of the ancient cathe drals; an edifice of three aisles, divided by piers and arches, and covered with vaulting.
Sir Christopher Wren has not only adopted the form of building practised by the architects of the middle ages. hut he has imitated their mode of construction ; for the lofty vault of the middle aisle is supported by flying buttresses concealed by an enormous screen wall. The architectural detail is in the Roman style, simple and regular.
"The Romans," says Sir Christoloher, " thougli they some times used a hemisphere, as in the exhedr•e of the baths, of the tribunes, of the temples, and basilica', yet, generally, they used a plain rylindricul 'mulling where the walls were parallel, or cross-vaulting where the two cylinders intersected in diagonals, as in the Temple of Peace. and in all the thea tres, in the passages under the steps. The moderns, whose arches are not circular, use commonly another sort, where the spandrels, resting upon the pillars, spring every way rotund as their arch rises in sections of circles, parallel to the horizon ; that is, in four quadrants described from the angles of a square, and terminated by its sides; and, at the summit, these quadrants come in contact in the middle of the sides, the four curves forming a quadrilateral, each side being con vex towards the centre; and the space thus included is filled with tracery work. which gives them great opportunity of
divers variations. which 1 need not insist on. Another way, (which I cannot find used by the ancients, hut in the latter Eastern empire, as appears at St. Sophia, and by the exam pies of all the mosques and cloisters of the Dervises, and UVOI'VW11C1.1 at present in the East. and of all others the most geometrical,) is confused of hemispheres and their sections only ; where, as a sphere may lie cut in manner of ways, and that still into circles, it may be accommodated to lie in all positions of the pillars. u Let A a c I) be a cupola, or hemisphere, resting upon four pillars, from whence arise the four verticut arches; to which the sections, being semi circles, lutist it 011 all sides, whether A a be 0111111 to 13 c or not : cut the 'hemisphere again horizontally, the section will be an entire circle, touching in the keys of the arches, and (4, k, 1. will be the spandrels, resting upon the pillars, yet still are parts of the hemisphere; and it' the hori zontal circle be taken away, you may build upon that circle an upright stay bear a cupola again above, as is done in St.. Sophia and St. Peter's, and in all the churches in Rome. I question not, but those at Constantinople had it from the Greeks betbre them. It is so natural, and is yet found in the present seraglio, which Was the palace of old ; the imperial palace, whose ruins still appear, being farther eastward. Now, because I have, Iler just reasons, followed this way of vaulting of the aura of St. Paul's. I think it proper to show that it is the lightest trimmer, and requires less hutment than the eross-vaulting, as well as it is of an agreeable view." We shall now proceed with the description of the other parts of this edifice.
It appears that these domes are of considerable antiquity, and, from the reasons here given from the Purentalia, that Sir Christopher Wren was justified in his choice in their adoption ; their fortn is beautiful ; and, when investigated, it is truly geometrical. Each wing forms a flat dome, sup ported by tour spandrels ; a rich Mreath of foliage encircles the base, while the centre and the spandrels allierd spaces well adapted. and probably intended, to receive ornamental paintings. The western transept is a part of the building; here insulated columns and screens of iron-railing separate from the aisles, on either side, the morning-prayer chapel, and the consistory.