Leonardo da Vinci, Pathfinder of Science

by Henry S. Gillette

Although Leonardo had found a haven of peace in the political storm that raged about the city state of Mantua, he and Pacioli took to the road again for reasons unknown. Isabella d’Este, who still wanted Leonardo at her court, sent many a letter and messenger in the following years to bring Leonardo back—first to finish the portrait and then, when that failed, to sell to her any picture that Leonardo wished to send. Strangely enough, however, Leonardo seems to have turned his back upon the one sympathetic person he had met in a world of indifference.

The first, warm breezes of spring were blowing over the lagoons of Venice when Leonardo and Pacioli stepped ashore on the Piazzetta, or Little Square of San Marco. But the beauty of this jewel-like city rising from the sea was momentarily ignored by the two travelers for an angry, frightened crowd had gathered about the Doge’s palace on the Piazzetta.

The people of Venice were fearful because their fleet had just suffered a crushing defeat by the Turks. This meant that their power at sea, once supreme, was now no more. Year by year, moreover, their possessions in the east had been slowly whittled away, and now the city itself was threatened by invasion. At this same time, the Venetian ambassador, Manenti, hoping to make peace with the Turks, had been rudely rejected by them. Panic soon swept the city and rumors of the bloodthirsty infidel passed from person to person like the rush of an ugly wind. Barricades were put up and windows were barred. In this charged atmosphere, Leonardo and Pacioli sought out their lodgings.

Soon after Leonardo’s arrival here—either because his reputation had preceded him or, more likely, because of Fra Luca Pacioli’s recommendations—he became directly involved with the defenses of Venice. Immediately he was sent on an inspection trip of the city’s existing defenses, especially those inland from where an invasion would probably come. When he had seen them, he recommended a system of defenses along the Isonzo river near the present border of Yugoslavia, using the river itself to the disadvantage of the enemy. He also made suggestions for the improvement of forts, and even drew up plans for a completely new type—a circular fort. This consisted of a central, circular fort surrounded by two belts of fortresses each separated by a moat. In the outside moat were four semicircular outposts. Communication was by underground galleries. The total absence of superstructure and projecting balconies was a new idea for the times. Another new defense idea was to station in the moat itself a low, thick tower almost completely submerged, defended by a thin opening near the waterline. It was reached from the main fort by an underground passage and the gunsmoke was removed by vents. According to Leonardo no enemy could conceal himself in any part of the defenses and not be seen from such an outpost.

Leonardo’s most unusual scheme for defending Venice, however, was his idea of approaching an enemy fleet under the water and then putting holes in the hulls of their ships. Actually, the idea of diving was not a new one. Aristotle had written of diving and diving bells, and certainly the stories of pearl fishers in the Orient were well known in the Renaissance. But Leonardo designed a diver’s suit closely resembling those used today. This consisted of a complete suit of leather with helmet and eyepieces; it was made airtight by spirals of steel at the joints. He then added a bladder for holding air which fastened inside the suit at the diver’s chest. It is possible that Leonardo also invented an air chamber that could be used by the diver while under water—but he was very secretive about this invention for fear of how men might abuse such a discovery. He wrote, “... and this I do not publish or divulge, on account of the evil nature of man, who would practice assassinations at the bottom of the seas....”

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.