Leonardo felt the same way about a “submarine” that he presented to the Councilors and Tribunal of Venice. This resembled a turtle’s shell with a raised bump on the center which was the “periscope.” When submerged the water probably rose to an area just around the “periscope,” but, again, the information about its air-supply is missing and the only reference to it is a reminder to close the “l—.” In addition, he invented a system of screws mounted in tongs with the borer in the middle for putting holes in the bottoms of enemy ships, and at the same time he thought of a defense against such an attack by designing the defending vessels with double hulls. Among Leonardo’s other maritime devices were designs for boats that could dredge canals, harbors, and lagoons. What was the result of all these plans? We do not know. Whether any one of them was used against the Turks is a mystery. At any rate, Leonardo and Pacioli left Venice that same spring and arrived in Florence in April of 1500. One of the purposes of Leonardo’s journey was to visit his father who was now living on Via Ghibellina with his fourth wife. Leonardo was now forty-eight. Still tall and straight with the strength of his youth, his face prematurely aged and his hair thinning back from his high forehead, Leonardo was more than ever an outstanding looking man. He still scorned fashionable clothes and dressed according to his own comfort which made him even more noticeable among the crowd. His deep-set eyes with their direct and penetrating glance, framed by his full, reddish beard, never missed a thing, although he now wore spectacles at his work. Now that he was back in Florence, Leonardo needed lodgings and a job. He had banked his small savings, and he did not want to touch that. His father’s house with the five children of his present wife plus the sons from his previous marriages was too full to accommodate Leonardo. Moreover, the relationship between Piero and Leonardo was polite but distant, as Piero preferred the children of his later marriages. Luckily, the place to live and the commission Leonardo needed presented themselves at the same time. The Church of the Annunciation of the Servite Order of Monks needed an altarpiece, and, as Leonardo’s fame was great, they offered him and his apprentice quarters in the monastery. Here, in the solitude of a monastic cell, Leonardo was able to return to his own researches. His long association with Fra Luca Pacioli continued as they worked together on Pacioli’s edition of Euclid’s _Elements_. At the same time, with his absorption in geometry, Leonardo commenced his studies of the transformation of solids; that is, changing the shape of something to another shape without diminishing or increasing its substance.