A remedy so that the wind does not turn the bird upside down.

I saw the bird turn upside down by the left wind, which entered above the wind with the left wing.

In all birds that fly high, in the raising of their wings those wings remain perforated, as is demonstrated in its place. And when those wings descend, they remain united; and so, the pressed and condensed air not yielding to the descent of the wings with the speed that the wing itself has, it is necessary that the bird rebound from such percussion, from which it rises, and is carried upward by the acquired impetus for as much space of height as the impetus that rebounded it has of life. And in this time the wings reopen and perforate themselves with the spaces interposed among the said feathers; and then with fury it lowers the wings again, reuniting the feathers, and so regains the impetus already lost. And in this way do all the birds that rise with straight motion, such as the lark and the like; and those birds that do not use such dilation of feathers, such as the birds of rapine, must have their elevation whirling, that is made like a screw, or, if you will, a circular motion.

The butterfly and many similar insect animals all fly with four wings, having those behind smaller than those in front, and those in front make in part a cover to those behind; and all these such kinds can rise with straight motion, because when such wings lift, they remain perforated, keeping the front wings much higher than those behind; and so it keeps them almost to the end of that impetus which drives it upward, and then, on lowering them, the larger wings join to the smaller, and so, descending, they regain new impetus. There are still other species of flying insects which fly with four equal wings, but these do not cover one another in descending, nor likewise in rising, and these cannot rise with straight motion.