Suppose the body to be the round object figured here and let the light be at the point a, and let the illuminated side of the object be b c and the eye at the point d: I say that, as lustre is every where and complete in each part, if you stand at the point d the lustre will appear at c, and in proportion as the eye moves from d to a, the lustre will move from c to n.
134.
OF PAINTING.
Heigh light or lustre on any object is not situated [necessarily] in the middle of an illuminated object, but moves as and where the eye moves in looking at it.
135.
OF LIGHT AND LUSTRE.
What is the difference between light and the lustre which is seen on the polished surface of opaque bodies?
The lights which are produced from the polished surface of opaque bodies will be stationary on stationary objects even if the eye on which they strike moves. But reflected lights will, on those same objects, appear in as many different places on the surface as different positions are taken by the eye.
WHAT BODIES HAVE LIGHT UPON THEM WITHOUT LUSTRE?
Opaque bodies which have a hard and rough surface never display any lustre in any portion of the side on which the light falls.