It was while they were struggling in the grip of this vast social melancholy, and anxiously craving some new vision by which to reinterpret or transcend the agony of the past, that the Fifth Men were confronted with a most unexpected physical crisis. It was discovered that something queer was happening to the moon; in fact, that the orbit of the satellite was narrowing in upon the earth in a manner contrary to all the calculations of the scientists.

The Fifth Men had long ago fashioned for themselves an all-embracing and minutely coherent system of natural sciences, every factor in which had been put to the test a thousand times and had never been shaken. Imagine, then, their bewilderment at this extraordinary discovery. In ages when science was still fragmentary, a subversive discovery entailed merely a reorganization of some one department of science; but by now, such was the coherence of knowledge, that any minute discrepancy of fact and theory must throw man into a state of complete intellectual vertigo.

The evolution of the lunar orbit had, of course, been studied from time immemorial. Even the First Men had learned that the moon must first withdraw from and subsequently once more approach the earth, till it should reach a critical proximity and begin to break up into a swarm of fragments like the rings of Saturn. This view had been very thoroughly confirmed by the Fifth Men themselves. The satellite should have continued to withdraw for yet many hundreds of millions of years; but in fact it was now observed that not only had the withdrawal ceased, but a comparatively rapid approach had begun.

Observations and calculations were repeated, and ingenious theoretical explanations were suggested; but the truth remained completely hidden. It was left to a future and more brilliant species to discover the connexion between a planet’s gravitation and its cultural development. Meanwhile, the Fifth Men knew only that the distance between the earth and the moon was becoming smaller with ever-increasing rapidity.

This discovery was a tonic to a melancholy race. Men turned from the tragic past to the bewildering present and the uncertain future.

For it was evident that, if the present acceleration of approach were to be maintained, the moon would enter the critical zone and disintegrate in less than ten million years; and, further, that the fragments would not maintain themselves as a ring, but would soon crash upon the earth. Heat generated by their impact would make the surface of the earth impossible as the home of life. A short-lived and short-sighted species might well have considered ten million years as equivalent to eternity. Not so the Fifth Men. Thinking primarily in terms of the race, they recognized at once that their whole social policy must now be dominated by this future catastrophe. Some there were indeed who at first refused to take the matter seriously, saying that there was no reason to believe that the moon’s odd behaviour would continue indefinitely. But as the years advanced, this view became increasingly improbable. Some of those who had spent much of their lives in exploration of the past now sought to explore the future also, hoping to prove that human civilization would always be discoverable on the earth in no matter how remote a future. But the attempt to unveil the future by direct inspection failed completely. It was surmised, erroneously, that future events, unlike past events, must be strictly non-existent until their creation by the advancing present.

Clearly humanity must leave its native planet. Research was therefore concentrated on the possibility of flight through empty space, and the suitability of neighbouring worlds. The only alternatives were Mars and Venus. The former was by now without water and without atmosphere. The latter had a dense moist atmosphere, but one which lacked oxygen. The surface of Venus, moreover, was known to be almost completely covered with a shallow ocean. Further the planet was so hot by day that, even at the poles, man in his present state would scarcely survive.

It did not take the Fifth Men many centuries to devise a tolerable means of voyaging in interplanetary space. Immense rockets were constructed, the motive power of which was derived from the annihilation of matter. The vehicle was propelled simply by the terrific pressure of radiation thus produced. ‘Fuel’ for a voyage of many months, or even years, could, of course, easily be carried, since the annihilation of a minute amount of matter produced a vast wealth of energy. Moreover, when once the vessel had emerged from the earth’s atmosphere, and had attained full speed, she would, of course, maintain it without the use of power from the rocket apparatus. The task of rendering the ‘ether-ship’ properly manageable and decently habitable proved difficult, but not insurmountable. The first vessel to take the ether was a cigar-shaped hull some three thousand feet long, and built of metals whose artificial atoms were incomparably more rigid than anything hitherto known. Batteries of ‘rocket’ apparatus at various points on the hull enabled the ship not only to travel forward, but to reverse, turn in any direction, or side-step. Windows of an artificial transparent element, scarcely less strong than the metal of the hull, enabled the voyagers to look around them. Within there was ample accommodation for a hundred persons and their provisions for three years. Air for the same period was manufactured in transit from protons and electrons stored under pressure comparable to that in the interior of a star. Heat was, of course, provided by the annihilation of matter. Powerful refrigeration would permit the vessel to approach the sun almost to the orbit of Mercury. An ‘artificial gravity’ system, based on the properties of the electro-magnetic field, could be turned on and regulated at will, so as to maintain a more or less normal environment for the human organism.

This pioneer ship was manned with a navigating crew and a company of scientists, and was successfully dispatched upon a trial trip. The intention was to approach close to the surface of the moon, possibly to circumnavigate it at an altitude of ten thousand feet, and to return without landing. For many days those on earth received radio messages from the vessel’s powerful installation, reporting that all was going well. But suddenly the messages ceased, and no more was ever heard of the vessel. Almost at the moment of the last message, telescopes had revealed a sudden flash of light at a point on the vessel’s course. It was therefore surmised that she had collided with a meteor and fused with the heat of the impact.

Other vessels were built and dispatched on trial voyages. Many failed to return. Some got out of control, and reported that they were heading for outer space or plunging towards the sun, their hopeless messages continuing until the last of the crew succumbed to suffocation. Other vessels returned successfully, but with crews haggard and distraught from long confinement in bad atmosphere. One, venturing to land on the moon, broke her back, so that the air rushed out of her, and her people died. After her last message was received, she was detected from the earth, as an added speck on the stippled surface of a lunar ‘sea’.

As time passed, however, accidents became rarer; indeed, so rare that trips in the void began to be a popular form of amusement. Literature of the period reverberates with the novelty of such experiences, with the sense that man had at last learned true flight, and acquired the freedom of the solar system. Writers dwelt upon the shock of seeing, as the vessel soared and accelerated, the landscape dwindle to a mere illuminated disc or crescent, surrounded by constellations. They remarked also the awful remoteness and mystery which travellers experienced on these early voyages, with dazzling sunlight on one side of the vessel and dazzlingly bespangled night on the other. They described how the intense sun spread his corona against a black and star-crowded sky. They expatiated also on the overwhelming interest of approaching another planet; of inspecting from the sky the still visible remains of Martian civilization; of groping through the cloud banks of Venus to discover islands in her almost coastless ocean; of daring an approach to Mercury, till the heat became insupportable in spite of the best refrigerating mechanism; of feeling a way across the belt of the asteroids and onwards toward Jupiter, till shortage of air and provisions forced a return.

But though the mere navigation of space was thus easily accomplished, the major task was still untouched. It was necessary either to remake man’s nature to suit another planet, or to modify conditions upon another planet to suit man’s nature. The former alternative was repugnant to the Fifth Men. Obviously it would entail an almost complete refashioning of the human organism. No existing individual could possibly be so altered as to live in the present conditions of Mars or Venus. And it would probably prove impossible to create a new being, adapted to these conditions, without sacrificing the brilliant and harmonious constitution of the extant species.

On the other hand, Mars could not be made habitable without first being stocked, with air and water; and such an undertaking seemed impossible. There was nothing for it, then, but to attack Venus. The polar surfaces of that planet, shielded by impenetrable depths of cloud, proved after all not unendurably hot. Subsequent generations might perhaps be modified so as to withstand even the sub-arctic and ‘temperate’ climates. Oxygen was plentiful, but it was all tied up in chemical combination. Inevitably so, since oxygen combines very readily, and on Venus there was no vegetable life to exhale the free gas and replenish the ever-vanishing supply. It was necessary, then, to equip Venus with an appropriate vegetation, which in the course of ages should render the planet’s atmosphere hospitable to man. The chemical and physical conditions on Venus had therefore to be studied in great detail, so that it might be possible to design a kind of life which would have a chance of flourishing. This research had to be carried out from within the ether-ships, or with gas helmets, since no human being could live in the natural atmosphere of the planet.

We must not dwell upon the age of heroic research and adventure which now began. Observations of the lunar orbit were showing that ten million years was too long an estimate of the future habitability of the earth; and it was soon realized that Venus could not be made ready soon enough unless some more rapid change was set on foot. It was therefore decided to split up some of the ocean of the planet into hydrogen and oxygen by a vast process of electrolysis. This would have been a more difficult task, had not the ocean been relatively free from salt, owing to the fact that there was so little dry land to be denuded of salts by rain and river. The oxygen thus formed by electrolysis would be allowed to mix with the atmosphere. The hydrogen had to be got rid of somehow, and an ingenious method was devised by which it should be ejected beyond the limits of the atmosphere at so great a speed that it would never return. Once sufficient free oxygen had been produced, the new vegetation would replenish the loss due to oxidation. This work was duly set on foot. Great automatic electrolysing stations were founded on several of the islands; and biological research produced at length a whole flora of specialized vegetable types to cover the land surface of the planet. It was hoped that in less than a million years Venus would be fit to receive the human race, and the race fit to live on Venus.

Meanwhile a careful survey of the planet had been undertaken. Its land surface, scarcely more than a thousandth that of the earth, consisted of an unevenly distributed archipelago of mountainous islands. The planet had evidently not long ago been through a mountain-forming era, for soundings proved its whole surface to be extravagantly corrugated. The ocean was subject to terrific storms and currents; for since the planet took several weeks to rotate, there was a great difference of temperature and atmospheric pressure between the almost Arctic hemisphere of night and the sweltering hemisphere of day. So great was the evaporation, that open sky was almost never visible from any part of the planet’s surface; and indeed the average daytime weather was a succession of thick fogs and fantastic thunderstorms. Rain in the evening was a continuous torrent. Yet before night was over the waves clattered with fragments of ice.

Man looked upon his future home with loathing, and on his birthplace with an affection which became passionate. With its blue sky, its incomparable starry nights, its temperate and varied continents, its ample spaces of agriculture, wilderness, and park, its well-known beasts and plants, and all the material fabric of the most enduring of terrestrial civilizations, it seemed to the men and women who were planning flight almost a living thing imploring them not to desert it. They looked often with hate at the quiet moon, now visibly larger than the moon of history. They revised again and again their astronomical and physical theories, hoping for some flaw which should render the moon’s observed behaviour less mysterious, less terrifying. But they found nothing. It was as though a fiend out of some ancient myth had come to life in the modern world, to interfere with the laws of nature for man’s undoing.