"True," I answered. "If it were solid I could not be a hundred miles beneath its surface in conversation with another being; but there can not be many such cavities as that which we are now traversing, and they can not surely extend entirely through its mass; the great weight of the superincumbent material would crush together the strongest materials, if a globe as large as our earth were extensively honeycombed in this manner." "Quite the contrary," he replied; "and here let me, for the first time, enlighten you as to the interior structure of the terrestrial globe. The earth-forming principle consists of an invisible sphere of energy that, spinning through space, supports the space dust which collects on it, as dust on a bubble. By gradual accumulation of substance on that sphere a hollow ball has resulted, on the outer surface of which you have hitherto dwelt. The crust of the earth is comparatively thin, not more than eight hundred miles in average thickness, and is held in position by the central sphere of energy that now exists at a distance about seven hundred miles beneath the ocean level. The force inherent to this sphere manifests itself upon the matter which it supports on both sides, rendering matter the lighter the nearer it lies to the center sphere. In other words, let me say to you: The crust, or shell, which I have just described as being but about eight hundred miles in thickness, is firm and solid on both its convex and concave surface, but gradually loses in weight, whether we penetrate from the outer surface toward the center, or from any point of the inner surface towards the outside, until at the central sphere matter has no weight at all. Do you conceive my meaning?" "Yes," I replied; "I understand you perfectly." After a pause my pilot asked me abruptly: "What do you most desire?" The question caused my mind to revert instantly to my old home on the earth above me, and although I felt the hope of returning to it spring up in my heart, the force of habit caused me involuntarily to answer, "More light!" "More light being your desire, you shall receive it." Obedient to his touch, the bow of the boat turned from the gulf we had been considering towards the center of the lake; the responsive craft leaped forward, and in an instant the obsidian parapet disappeared behind us. On and over the trackless waste of glass-like water we sped, until the dead silence became painfully oppressive, and I asked: "Whither are we bound?" "Towards the east."