"The louder a sound is, the more we recognize it as being near, so the louder the "tone" of objects that is, the blacker or whiter the nearer they seem; and so if in our picture we wish to give a sense of distance, we must see that the darkest shadows and highest lights are in the foreground : and because we may not be able to materially alter things as the undiscriminating process gives them to us, we must seek for and select those scenes, those subjects, in which this arrangement of highest and deepest tones do come in the foreground, and then take care that our process renders them with fidelity, so that we may not lose the sense of their nearness or the feeling of greater distance of other planes which it is intended they shall give."