The Marquis Poleni of Padua, a distinguished engineer of the time, was then called to examine the dome and to take such means as he might judge most effective to secure it against further disintegration. Milizia tells us[58] that Poleni, after careful examination, expressed the opinion that although the cupola had not the catenary outline which he considered the best for stability, it had nevertheless a good form, and was in no danger of ruin. He pronounced the fissures of no material consequence,[59] and attributed them to two classes of causes. The first of these he thought was haste in construction. The dome having been built in twenty-two months with materials of unequal quality, and not carefully laid, unequal consolidation resulted and caused numerous ruptures. The second class of causes he considered to consist in the action of heat and cold, humidity and dryness, lightning and earthquake. Thus far, says Milizia, the reasoning of Poleni is just, and worthy of his great mind, and he adds, “It would seem, then, that since the cupola was solid, it ought to have been left in peace, but he nevertheless advised five chains, which were placed under the direction of Vanvitelli.”[60] The first of these chains was located at the base of the drum, the second at the level of the attic, the third at the springing of the dome, the fourth above the haunch, and the fifth around the opening at the base of the lantern. [Illustration: Plate III DOME OF ST. PETER’S Rome] Poleni, in his own book, is not wholly consistent in what he says of the dome. While affirming its form to be admirable and its strength sufficient, and attributing the ruptures to other causes than those inherent in the nature of the design, he yet, in another place, admits that they may be to some extent due to the shape of the vault which he here pronounces not high, or acute, enough.[61] His admiration for Michael Angelo makes it hard for him, as a rule, to find any radical defect in the composition; but this passage, and the fact that he caused the additional binding chains to be applied, would seem to show that he had misgivings, and did not consider the monument so entirely safe as the general tenor of his book would lead us to believe. And the same misgivings are betrayed in what is said by the numerous other writers whose opinions are cited by him, though like himself they write for the most part with a manifest bias in favour of Michael Angelo. Thus one of these writers proposes that the outer covering of lead should be stripped off on account of its weight, and be replaced with copper, to which Poleni objects,[62] affirming that the weight is an advantage, and tends to hold the dome together. Another writer suggests that the lantern be removed in order to relieve the fabric of its weight. Another thinks that the buttresses should be heavily weighted with statues. It was also proposed that additional buttresses should