The Crossing of the Winds and the Birth of Lightning
Red-chalk notes on winds rising from cloud, colliding, and generating thunderbolts
Under the theme 'crossing of the winds', Leonardo describes how winds that rise from a cloud keep their motion and climb ever higher into the thinner air, where they meet less resistance. When such winds collide they rebound backward, and in these collisions lightning bolts are generated. He closes with a question: if a wind is born down below, what drives it more toward the east than toward the west? A faint red-chalk sketch of the winds runs across the top of the page.
On this page
Winds rising into thin air and colliding
Winds raised from a cloud continue their motion, and the more they move the higher they rise into thinner air, where they are less impeded. Where two such winds collide they rebound, and in the shock lightning bolts are born. Leonardo then asks what should drive a low-born wind more to the east than to the west.
Motion, rebound and resistance of moving air
The passage treats wind as a moving body governed by resistance and reflection: it accelerates upward where the medium is thinner, and rebounds when two currents meet head-on. The collision of currents is offered as the mechanical cause of lightning.