One should not desire the impossible.

a - n - c b - m - f o d

x y a - b - c - d - K c - t S p q n - i h g f v m

That luminous body of long and narrow shape makes the boundaries of the derivative shadow more confused than the spherical light does, and this is what contradicts the following proposition: that shadow will have its boundaries more distinct which is nearer to the primitive shadow, or, if you will, to the shadowing body; but the cause of this is the long shape of the luminous body a c, etc.

Of light and lustre.

What difference is there between light and lustre, which shows itself on the polished surfaces of opaque bodies.

The lights that are generated on the polished surfaces of opaque bodies will be immobile on immobile bodies, even though the eye of the viewer moves. But the lustres will be upon those same bodies in as many places of its surface as are the sites where the eye moves.

Which places are those that have light without lustre.

The opaque bodies that have a dense and rough surface never generate lustre in any place of their illuminated part.

Which bodies are those that have lustre and not luminous parts.

The dense opaque bodies with a dense surface are those that have all the lustre in as many places of the illuminated part as are the sites that can receive the angle of incidence of the light and of the eye; but because such a surface mirrors all the things surrounding the light, the illuminated part is not recognized in that part of the illuminated body.