During this conversation we had been rapidly walking, or I should better say advancing, for we no longer walked as men do, but skipped down into the earth, down, ever downward. There were long periods of silence, in which I was engaged in meditating over the problems that successively demanded solution, and even had I desired to do so I could have kept no record of time; days, or even weeks, may have been consumed in this journey. Neither have I any method of judging of the rapidity of our motion. I was sensible of a marked decrease in the amount of muscular energy required to carry us onward, and I realized that my body was quite exempt from weariness. Motion became restful instead of exhausting, and it seemed to me that the ratio of the loss of weight, as shown by our free movements, in proportion to the distance we traversed, was greater than formerly. The slightest exhibition of propelling force cast us rapidly forward. Instead of the laborious, short step of upper earth, a single leap would carry us many yards. A slight spring, and with our bodies in space, we would skip several rods, alighting gently, to move again as easily. I marveled, for, although I had been led to anticipate something unusual, the practical evidence was wonderfully impressive, and I again questioned my guide. "We are now nearing what physicists would call the center of gravity," he replied, "and our weight is rapidly diminishing. This is in exact accordance with the laws that govern the force called gravitation, which, at the earth's surface, is apparently uniform, though no instrument known to man can demonstrate its exact variation within the field man occupies. Men have not, as yet, been in a position to estimate this change, although it is known that mountains attract objects, and that a change in weight as we descend into the earth is perceptible; but to evolve the true law, observation, at a distance of at least ten miles beneath the surface of the ocean is necessary, and man, being a creature whose motions are confined to a thin, horizontal skin of earth, has never been one mile beneath its surface, and in consequence his opportunities for comparison are extremely limited." [Illustration: "WE WOULD SKIP SEVERAL RODS, ALIGHTING GENTLY."] "I have been taught," I replied, "that the force of gravitation decreases until the center of the earth is reached, at which point a body is without weight; and I can scarcely understand how such positive statements from scientific men can be far from the truth."