The eye transmits its own image through the air to all the objects which face it, and also receives them on its own surface, whence the "sensus communis" takes them and considers them.

Light is the chaser away of darkness. Shade is the obstruction of light. Primary light is that which falls on objects and causes light and shade. And derived lights are those portions of a body which are illuminated by the primary light. A primary shadow is that side of a body on which the light cannot fall.

The eye which finds itself in the centre between the shadows and the lights that surround the shaded bodies, will see in these bodies thegreater shadows that are in them meeting themselves within equal angles that is of the visual incidence.

The eye encompasses the beauty of the whole world.

There are three aspects to perspective. The first has to do with how the size of objects seems to diminish according to distance: the second, the manner in which colors change the farther away they are from the eye; the third defines how objects ought to be finished less carefully the farther away they are.

Here forms, here colours, here the character of every part of the universe are concentrated to a point; and that point is so marvellous a thing ... Oh! marvellous, O stupendous Necessity - by thy laws thou dost compel every effect to be the direct result of its cause, by the shortest path. These are miracles.