“See how the wings, striking against the air, sustain the heavy eagle in the thin air on high,” he noted, then added, “As much force is exerted by the object against the air as by the air against the object.”16 Two hundred years later, Newton would state a refined version of this as his third law of motion: “To every action there is always opposed an equal reaction.”

“See how the wings, striking against the air, sustain the heavy eagle in the thin air on high,” he noted, then added, “As much force is exerted by the object against the air as by the air against the object.”16 Two hundred years later, Newton would state a refined version of this as his third law of motion: “To every action there is always opposed an equal reaction.”

— Walter Isaacson