The difficulty of giving surface to smooth water.

I believe it is a result of the experience of all artists, that it is the easiest thing in the world to give a certain degree of depth and transparency to water; but that it is next to impossible, to give a full impression of surface. If no reflection be given, a ripple being supposed, the water looks like lead: if reflection be given, it, in nine cases out of ten, looks morbidly clear and deep, so that we always go down into it, even when the artist most wishes us to glide over it. Now, this difficulty arises from the very same circumstance which occasions the frequent failure in effect of the best-drawn foregrounds, noticed in Section II. Chapter IV., the change, namely, of focus necessary in the eye in order to receive rays of light coming from different distances.

Is dependent on the structure of the eye, and the focus by which the reflected rays are perceived.

Go to the edge of a pond in a perfectly calm day, at some place where there is duckweed floating on the surface, not thick, but a leaf here and there. Now, you may either see in the water the reflection of the sky, or you may see the duckweed; but you cannot, by effort, see both together.