The Physics of Gliding Birds and Figures in Motion
Centre of gravity and support in moving bodies, with a note on reflected colour
This page opens by completing a rule on colour, telling the painter to mix into an object's shadow at a b as much of the reflected colour of the wall above (a d) as it shares. It then turns to motion: a figure shows greater speed the more it stands ready to topple forward, and a body that moves by itself is the faster the more the centre of its gravity is distant from the centre of its support. Leonardo applies this to birds that glide without beating their wings, explaining that when the centre of gravity a b lies outside the middle of the wings' resistance c d, the bird descends forward and obliquely.
On this page
Mixing the wall's reflected colour into an object's shadow
Where the greatest shadows terminate on the object the surface begins to lighten, as at n o, which keeps as much of the dark as it shares of the wall above, a d. That colour is to be mixed with the first shadow a b, using the same gradations.
A figure appears to move faster the more it topples forward
On the motion and course of animals: that figure will show itself of greater course, or speed, which stands more ready to topple forward.
A self-moving body is faster the farther its centre of gravity from its support
The body that moves by itself will be the faster the more the centre of its gravity is distant from the centre of its support. This happens when the centre of gravity a b lies outside the centre of the support c d, that is, outside the middle of the resistance of the wings.
How a bird glides forward without beating its wings
This is said of birds that move by themselves without beating their wings or the favour of wind: when the middle of the wings is farther back than the bird's centre of gravity, the bird moves forward and downward, and the more remote that centre is from the middle of the wings, the more oblique its descent.