Page:A Treatise on Painting.djvu/150

 raise the animal when they become straight and perpendicular upon the ground.   motion performed by a man, or any other animal whatever, in walking, will have more or less velocity as the centre of their weight is more or less removed from the centre of that foot upon which they are supported.   figure will appear the swiftest in its course which leans the most forwards.

Any body, moving of itself, will do it with more or less velocity in proportion as the centre of its gravity is more or less removed from the centre of its support. This is mentioned chiefly in regard to the motion of birds, which, without any clapping of their wings, or assistance of wind, move themselves. This happens when the centre of their gravity is out of the centre of their support, viz. out of its usual residence, the middle between the two wings. Because, if the middle of the wings be more backward than the centre of the whole weight, the bird will move forwards and downwards, in a greater or less degree as the centre of its weight is more or less removed from the middle of its wings. From which it follows, that if the centre of gravity be far removed from the other centre, the descent of the bird will be very oblique; but if that centre be near the middle Rh