Geometry of the Dome of the School of Nª Sª de la Antigua.

The shape of the dome is hemispherical, the average orange characteristic of the Spanish Renaissance. Its light is approximately 10 m and the key of the dome of its torch rises just over 35 m above the level of the pavement. The inner surface is slightly banked. It is reinforced by eight double ribs that protrude both inside and outside. The outer surface, also hemispherical, is not concentric with the interior, but its center moves downwards. The thickness is, therefore, variable and decreases as it rises.
The lantern rises above the oculus, with six windows, covered by a semi-spherical and banked dome. The dome is surrounded by a balustrade and is completed with a high pyramidal pinnacle with a square base topped with a metal cross with a weather vane. The drum that supports the dome is cylindrical. Its interior surface is uniform throughout its height, but its backyard, however, shows two distinct parts. In the lower one, from the cornice to the level of the trestle of the roof, the extrados is octagonal and the structure robust, while in the upper part the wall is noticeably thinned and its transverse, cylindrical in this area, rises and reaches a higher level than that of the imposts of the interior orange stocking. Dome and drum are set on an inner circular cornice, and is on the set of four pendentives and four arches and pillars torales.
(Taken from ROSA ANA GUERRA PESTONIT Arquitecta).