Note 24 — Chapter II · THE DOME OF FLORENCE

These ruptures were first observed in the year 1693 (Nelli, _op. cit._, p. 13), and it was then advised by the architect Carlo Fontana to add a new chain of iron. Nelli, however, argued that the fissures had not arisen from thrust, but were due to a slight yielding of the foundations, and he urged that no chain be added, but that a bit of marble be dove-tailed into the vault across the opening, in order that any further movement might be detected by the breaking of this marble. For three years no further sign of disturbance was noticed, but a slight earthquake in 1697 broke a portion of the masonry of the outer face of the dome opposite the fissure across which the marble had been placed. It appears, however, to have been concluded that there was still no danger from thrust, and no new chain was inserted. Cecchini (_Opinione intorno lo Stato della gran Cupola del Duomo di Firenze_, published together with Nelli’s _Discorsi_, etc., p. 82) speaks of several cracks in both the inner and the outer shells of the vault, and also in the supporting piers, even down to the ground. But he agrees with Nelli in attributing these to movements of the foundations from which he concludes that no further danger is to be apprehended, and he affirms that the structure is entirely safe.