The Birth of the Wind and Its Curving Path
Red-chalk note that wind follows the shortest way and bends toward thinner air
Headed 'Of the birth of the wind', this red-chalk page argues that every moving body follows its motion by the shortest way and flees or is deflected by obstacles. Applying this to air, Leonardo says the wind curves as it penetrates the thick lower air and bends upward toward the thinner air above. A caption records a sketch of the wind's trajectory with birds in flight, and a faint red-chalk arc runs across the upper page.
On this page
The wind bends from thick air toward thin
The wind, like any moving body, seeks the shortest path and is turned aside by whatever impedes it. So it curves as it drives through the dense lower air and then bends upward into the thinner air. The heading frames this as an account of how the wind is born.
Shortest-path motion and deflection
The note states a general principle: every mobile follows its motion by the briefest route and either flees an obstacle or is bent by it. Air is then treated as such a mobile, its curvature explained by the changing density of the medium it crosses.