Here again our other senses must assist us, notwithstanding in this chapter we shall be more confined to what is communicated to the eye by rays of light; and tho' things must now be consider'd as appearances only; produced and made out merely by means of _lights, shades,_ and _colours_. By the various circumstances of which, every one knows we have represented on the flat surface of the looking-glass, pictures equal to the originals reflected by it. The painter too, by proper dispositions of lights, shades, and colours, on his canvas, will raise the like ideas. Even prints, by means of lights and shades alone, will perfectly inform the eye of every shape and distance whatsoever, in which even lines must be consider'd as narrow parts of shade, a number of them, drawn or engrav'd neatly side by side, called _hatching_, serve as shades in prints, and when they are artfully managed, are a kind of pleasing _succedaneum_ to the delicacy of nature's. Could mezzo-tinto prints be wrought as accurately as those with the graver, they would come nearest to nature, because they are done without strokes or lines. I have often thought that a landskip, in the process of this way of representing it, doth a little resemble the first coming on of day. The copper-plate it is done upon, when the artist first takes it into hand, is wrought all over with an edg'd-tool, so as to make it print one even black, like night: and his whole work after this, is merely introducing the lights into it; which he does by scraping off the rough grain according to his design, artfully smoothing it most where light is most required: but as he proceeds in burnishing the lights, and clearing up the shades, he is obliged to take off frequent impressions to prove the progress of the work, so that each proof appears like the different times of a foggy morning, till one becomes so finish'd as to be distinct and clear enough to imitate a day-light piece. I have given this description because I think the whole operation, in the simplest manner, shews what lights and shades alone will do. As light must always be supposed, I need only speak of such privations of it as are called shades or shadows, wherein I shall endeavour to point out and regularly describe a certain order and arrangement in their appearance, in which order we may conceive different kinds of softnings and modulations of the rays of light which are said to fall upon the eye from every object it sees, and to cause those more or less-pleasing vibrations of the optic nerves, which serve to inform the mind concerning every different shape or figure that presents itself.