Since I mentioned in my last that Light did disturb the figures of External objects presented in Transparent bodies; you were pleased to ask, Whether light doth penetrate transparent bodies? I answer, for anything I know, it may; for when I consider the subtil, piercing and penetrating nature of light, I believe it doth; but again, when I consider that light is presented to our sight by transparent bodies onely, and not by duskish and dark bodies, and yet that those duskish bodies are more porous then the transparent bodies, so that the light hath more passage to pass through them, then through transparent bodies; but that on the contrary, those dark bodies, as Wood, and the like, do quite obscure the light, when as transparent bodies, as Glass, &c. transmit it, I am half perswaded that the transparent bodies, as Glass, rather present the Light by patterning it out, then by giving it passage: Also I am of a mind, that the air in a room may pattern out the Light from the Glass, for the Light in a room doth not appear so clear as in the Glass; also if the Glass be any way defective, it doth not present the Light so perfectly, whereas, if it were the penetration of light through the glass, the light would pass through all sorts of glass alike, which it doth not, but is more clearly seen through some, and more obscurely through others, according to the goodness or purity of the glass. But you may say, that the light divulges the imperfection or goodness of the glass; I answer, so it doth of any other objects perceived by our sight; for light is the presenter of objects to the sense and perception of sight, and for any thing I know, the corporeal optick motions make the figure of light, the ground figure of all other figures patterned out by the corporeal optick motions, as in dreams, or when as some do see in the dark, that is, without the help of exterior light. But you may say, That if the glass and the air in a room did pattern out the figure of light, those patterns of light would remain when light is absent: I answer, That is not usual in nature; for when the object removes, the Pattern alters; I will not say but that the corporeal optick motions may work by rote without objects, but that is irregular, as in some distempers. And thus, _Madam_, I have given you my opinion also to this your question; if you have any more scruples, I pray let me know of them, and assure your self that I shall be ready upon all occasions to express my self, Madam, _Your humble and faithful Servant._ XXVII. _MADAM,_