Trois dialogues entre Hylas et Philonous

otherwise than by impulse. A distant object therefore cannot act on the eye; nor consequently make itself or its properties perceivable to the soul. Whence it plainly follows that it is immediately some contiguous substance, which, operating on the eye, occasions a perception of colours: and such is light. PHIL. Howl is light then a substance? HYL. . I tell you, Philonous, external light is nothing but a thin fluid substance, whose minute particles being agitated with a brisk motion, and in various manners reflected from the different surfaces of outward objects to the eyes, communicate different motions to the optic nerves; which, being propagated to the brain, cause therein various impressions; and these are attended with the sensations of red, blue, yellow, &c. PHIL. It seems then the light doth no more than shake the optic nerves. HYL. Nothing else. PHIL. And consequent to each particular motion of the nerves, the mind is affected with a sensation, which is some particular colour. HYL. Right. PHIL. And these sensations have no existence without the mind. HYL. They have not. PHIL. How then do you affirm that colours are in the light; since by LIGHT you understand a corporeal substance external to the mind? HYL. Light and colours, as immediately perceived by us, I grant cannot exist without the mind. But in themselves they are only the motions and configurations of certain insensible particles of matter. PHIL. Colours then, in the vulgar sense, or taken for the immediate objects of sight, cannot agree to any but a perceiving substance. HYL. That is what I say. PHIL. Well then, since you give up the point as to those sensible qualities which are alone thought colours by all mankind beside, you may hold what you please with regard to those invisible ones of the philosophers.…