Nay, the very smallest things of their kind, the slightest water-colour sketch of Turner, a half-finished clay sketch of Donatello, the little song done in the corner of a provincial paper by a working clerk in a true poetic hour, are not to be fathomed by the most far-descending plummet of the scientific understanding.

These things are in that superphysical world into which, however closely he saw and dealt with his characters in the world of the senses, the conscience, or the understanding, Browning led them all at last.
The first of these poems is _Natural Theology on the Island; or, Caliban upon Setebos_.

Caliban, with the instincts and intelligence of an early savage, has, in an hour of holiday, set himself to conceive what Setebos, his mother's god, is like in character.

He talks out the question with himself, and because he is in a vague fear lest Setebos, hearing him soliloquise about him, should feel insulted and swing a thunder-bolt at him, he not only hides himself in the earth, but speaks in the third person, as if it was not he that spoke; hoping in that fashion to trick his God.
Browning, conceiving in himself the mind and temper of an honest, earthly, imaginative savage--who is developed far enough to build nature-myths in their coarse early forms--architectures the character of Setebos out of the habits, caprices, fancies, likes and dislikes, and thoughts of Caliban; and an excellent piece of penetrative imagination it is.

Browning has done nothing better, though he has done as well.
But Browning's Caliban is not a single personage.