No scientist before Leonardo had methodically shown how birds stay aloft. Most had simply embellished on Aristotle, who mistakenly thought that birds were supported by air the way ships were by water.12 Leonardo realized that keeping aloft in air requires fundamentally different dynamics than doing so in water, because birds are heavier than air and are thus subject to being pulled down by gravity. The first two folios of his Codex on the Flight of Birds deal with the laws of gravity, which he calls the "attraction of one object to another." The force of gravity, he wrote, acts in the direction of "an imaginary line between the centers of each object."13 He then described how to calculate the center of gravity of a bird, a pyramid, and other complex shapes.
( Walter Isaacson )
[ Leonardo da Vinci ]
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