But suppose we should gradually lose our speed and stop in a neutral point, how should I know it? The Earth now was, and had been for ten days, a mere spot on the Sun. While Mars had been visible, he had never increased in size in the telescope, and he was now invisible. The only way I could tell would be to wait until after many days had elapsed, and if Mars did not finally come into view, I should know something was wrong. But it would be too late then; there would be no winds or tides, no weight or buoyancy, nothing to move us out of that dreadful calm where even gravity does not exist. That must be avoided at every cost! But might we not be very near it now? Weight had been practically nothing for a month, within an hour it might be positively nothing, and---- The doctor's mutterings interrupted these thoughts. "The power with which to travel was so simple and so vast! It all lay hidden in that elementary law of magnetism, like poles repel and unlike poles attract. But the road to travel and the problems by the way, those were the hard things!" He was putting them all in the past tense, as if he had already solved them! But what was that law of magnetism he mentioned? Perhaps he would reveal his secrets to me in his ravings! I must mark every word he said; for it was clear I must solve the problem, he would not be well in time. I must brush the cobwebs from my meagre science and struggle with his invention. "Unlike poles attract," he had said. Then Earth and matter must normally have unlike poles, and to make Earth repel matter it would only be necessary to change the polarization of the matter. Yes, he had told me it was all accomplished by polarizing the steel and iron of the projectile! When they were made the same pole as the Earth, then she repelled them. But if the whole thing were so simple, why had it never been discovered before? Ah, that is the strong shield behind which incredulity always takes refuge!