The lights which may illuminate opaque bodies are of 4 kinds. These
are: diffused light as that of the atmosphere, within our horizon.
And Direct, as that of the sun, or of a window or door or other
opening. The third is Reflected light; and there is a 4th which is
that which passes through [semi] transparent bodies, as linen or
paper or the like, but not transparent like glass, or crystal, or
other diaphanous bodies, which produce the same effect as though
nothing intervened between the shaded object and the light that
falls upon it; and this we will discuss fully in our discourse.
Definition of the nature of shadows (119--122).
119.