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 factor in the prublem. I had satisfied myself that only one thing needful was as yet wholly beyond the reach and even the proximate hopes of science. Human invention could furnish as yet no motive power that could fulfil the main requirement of the problem—uniform or constantly increasing motion in vacuo—motion through a region affording no resisting medium. This must be a repulsive energy capable of acting through an utter void. Man, animals, birds, fishes move by repulsion applied at every moment. In air or water, paddles, oars, sails, fins, wings act by repulsion exerted on the fluid element in which they work. But in space there is no such resisting element on which repulsion can operate. I needed a repulsion which would act like gravitation through an indefinite distance and in a void—act upon a remote fulcrum, such as might be the Earth in a voyage to the Moon, or the Sun in a more distant journey. As soon, then, as the character of the apergic force was made known to me, its application to this purpose seized on my mind. Experiment had proved it possible, by the method described at the commencement of this record, to generate and collect it in amounts practically unlimited. The other hindrances to a voyage through space were trivial in comparison with that thus overcome; there were difficulties to be surmounted, not absent or deficient powers in nature to be discovered. The chief of these, of course, concerned the conveyance of air sufficient for the needs of the traveller during the period of his journey. The construction of an air-tight vessel was easy enough; but however large the body of air conveyed, even