Michelagnolo has ordered to be constructed of well-baked bricks, the thickness given to the wall being four palms and a half above as well as below, leaving a space in the middle which is four palms and a half wide at the foot, and this is to be occupied by the stairs leading from the cornice, whereon are the balustrades, to the lantern; the arch of the interior of the second vaulting, which is broader below and narrower above, proceeds from the point B, which gives four palms and a half as the thickness of the lower part. The last arch which represents the outer side, and is also enlarged below while it is restricted above, departs from the point A.[1] At the upper part this arclf' gives the entire space in which are the stairs, whose height is of eight palms, so that men can walk upright therein, the thickness of the vault being gradually diminished to the extent that, while it has four palms and a half at the foot, it has three palms and a half only at the head. The vaultings, exterior and interior, are so well conjoined and connected that one supports the other; of the eight parts into which it is divided at the base, four are left hollow above the arches, to diminish the weight, while the four others are bound and 'secured to the piers in such sort that their durability may well extend to all time.
The central stairs between the two vaultings are made in the following manner. Those which start from the point whence the vault springs have each two branches, and proceeding through one of the sections they cross each other inr the form of the letter X, until they attain the summit of the vaulting over the centre of the arch C. Having thus ascended the half of this arch by a direct line, the remainder is commodiously surrounded by a flight which turns easily, until the summit, whence the lantern commences, is attained; around this there is a smaller range of double pilasters and windows similar to those in the interior, all corresponding with that diminution of the compartments which takes place above the piers, as will be described below.
Over the flrst great cornice within the tribune commence those concave compartments into which the vaulting is divided and which are formed by sixteen projecting ribs; these have
- ↑ The complaints of all commentators, Italian and German alike, as to the obscurity of this description, are here renewed with increased energy, but the elucidations they attempt cannot be reproduced in this place, and we content ourselves with referring our reader to the authorities before cited.
