The dome of St. Mark, at Venice, erected about the year 97,3, and that of the cathedral at Pisa, built early in the eleventh century, are both upon the same plan with the pre ceding. The church of Saint 'Afark, built in the tenth century, has five domes; the central (ionic much larger than t he ot hers. Each dome is enclosed four pieces of semi-cylindrical vaulting together limning a square ; in the angles of this square are four corbels.which gather in the circular base of each dome. In 1523. Sansovinns, the archi tect. repaired the great dome, and placed a circle of iron round it to prevent its falling. A similar precaution was taken with one of the smaller domes by Andrew Tirali, in 1735, with the same successful result.
The dome of San Vitale at Ravenna, is of very curious con struction. The plan of the lower part is that of a regular octagon, supported by eight piers at the angles of the dome. Between these angles are seven tall niches divided into two stories. The lower part of these niches is open, and adorned with columns. The remaining side of the dome is an arch of the smile diameter and elevation as the niches; this arch f•m ing an entrance. Above these the wall sustains a hemi spherical dome, the plan being a circle within an octagon. Corbels are not employed at Santa Sophia, but the arches support the gathering over, which fornis the circular base of the dome. In the base are eight windows, each window being divided in the Centre by a column supporting two small arches. The dome itself is built with a double row of pipes, hollow' at one end and pointed at the other, so that the point of one is received in the hollow of the preceding one, continuing thus in a spiral line until they finish at the top. Both the exterior and the interior of the dome are covered with tnortar.
In 1298, the cathedral of Santa Maria del Fiore, was begun at Pisa, by the celebrated Arnolfo Lusii ; but he died two Year.; after, and no architect could be found who would under take to execute the dome upon the vast plan that its pro jector had designed : it consequently remained unfinished for one hundred and twenty years ; when, in a professional con vocation, Philip Brunellesehi was permitted to attempt its completion. (See BRUNELLESC111.) Notwithstanding the opposition he met with, and the vapouring sarcasms with which he was treated by his contemporaries, who held his scheme to be impracticable, he earrieq, on the building, and completed the cupola, in a manner worthy of his great repu tation. This dome, which is octangular, and of great elevation, is formed of'two vaults, with a vacancy between them; and is supported merely by the springing wall, without the aid of buttresses, though its dimensions exceed those of all the ancient Roman domes, with the sole exception of that of St. Peter's.
The church of St. Peter's, at Rome, is the largest temple ever built : it was begun by Bramante, in 1513, and carried on successively by Raphael, San Gallo, and Michael Angelo, the latter of whom designed the dome as it now appears. The following description, extracted from the " Encylop6die ethodique," and the " Penny Cycloptedia,'! will enable the reader to form sonic idea of this superb work.
"The dome, which is double, is circular on the plan. The internal dome is constructed on double consoles, instead of corbellings. The double consoles are crowned with a small cornice, forming an impost tor eight arches, from the upper part of which springs the dome; on the top is a lantern light, which is not apparent externally. Up to this time domes had been constructed on walls and corbellings, but in St. Peter's at Home a new plan was adopted. The dome of St. Peter's stands upon four piers, 61 feet 11 inches high, and 30 feet 10 inches thick, measured in a straight line with the arches. From the arches spring the corbellings, which are finished by an entablature. Upon this entablature is a plinth. The plinth is externally an octagon, and internally a circle. The external diameter of the octagon is 192 feet 9 inches, and the internal circle 134 feet 84 inches ; the thinnest part of the wall, between the octagon and the circle, is 29 feet 3 inches. On the plinth is a circular stylobate, 28 feet 6:1- inches thick. This thickness is divided into three parts by a circular passage 5 feet 10 inches wide; the two walls on each side of this passage are, respectively, the internal wall 14 feet 7k inches thick, and the external S feet. In the internal wall are other smaller passages, 2 feet 10 inches wide, Iltrining flights of steps communicating with the four spiral staircases formed in the thickness of the wall of the drum of the dome. Above the circular stylobate, which is 12 feet inches high, is placed the drum of the dome, which is 10 feet 1f inch thick, measured to the inside line of the pilasters, which decorate the interior of the dome. The pilasters them selves are 1.78 feet thick in addition. The construction is formed of rubble and fragments of brick. The interior is formed with bricks stuccoed. Externally the work is faced with thin slabs of travertine stone. The 11111111 is pierced With 16 windows. 9 feet inches wide, and 17 feet high. The walls arc strengthened 011 the between the with 16 buttresses. elmstml1C1 ell With masonry. These buttresses are 13 feet 3 incites wide. and 51 feet 6 inches in height from the base to the top of the entablature. Each buttress is decorated and strengthened with half-pilasters, and terminates with • two coupled columns engaged, the diameter of which is 4 feet ; the order is W hen the base of the dome had been built to the height of the entablature of the drum. .Miehael Angelo died ; but some time before his death he had caused a model to be made, with ample details, to which he added drawings and instructions. After his death Pirro Ligorio and Viiontla were appointed the architects. Giaeohto della Porta, the pupil of Vignola. 1b1 lowed his master as architect to the cathedral ; but although the designs of Michael Angelo were strictly f dlowed, the dome itself' was constructed under the pontificate of Sixtus V. Sixtus gave Giacomo della Porta as a colleague, Domenico Fontana, by W hem the dome was constructed.