Explanation

‘So far as I could see, all the world displayed the same exuberant richness as the Thames valley. From every hill I climbed I saw the same abundance of splendid buildings, endlessly varied in material and style; the same cluttering thickets of evergreens, the same blossom-laden trees and tree ferns. Here and there water shone like silver, and beyond, the land rose into blue undulating hills, and so faded into the serenity of the sky. A peculiar feature, which presently attracted my attention, was the presence of certain circular wells, several, as it seemed to me, of a very great depth. One lay by the path up the hill, which I had followed during my first walk. Like the others, it was rimmed with bronze, curiously wrought, and protected by a little cupola from the rain. Sitting by the side of these wells, and peering down into the shafted darkness, I could see no gleam of water, nor could I start any reflection with a lighted match. But in all of them I heard a certain sound: a thud—thud—thud, like the beating of some big engine; and I discovered, from the flaring of my matches, that a steady current of air set down the shafts. Further, I threw a scrap of paper into the throat of one; and, instead of fluttering slowly down, it was at once sucked swiftly out of sight.