Note 110 — AËRONAUTICS.
Reading edition
It is clear from the above that Borelli did not know that the wings of birds strike forwards as well as downwards during the down stroke, and forwards as well as upwards during the up stroke. These points, as well as the twisting and untwisting figure-of-8 action of the wing, were first described by the author. Borelli seems to have been equally ignorant of the fact that the wings of insects vibrate in a more or less horizontal direction.