So far, those who have considered spatial navigation have regarded it from the point of view of exploration and planetary visitation, but the vast importance of escaping from the earth's gravitational field has been almost entirely overlooked. On earth, even if we should use all the solar energy which we received, we should still be wasting all but one two-billionths of the energy that the sun gives out. Consequently, when we have learnt to live on this solar energy and also to emancipate ourselves from the earth's surface, the possibilities of the spread of humanity will be multiplied accordingly. We can imagine this occurring in definite stages. When the technicalities of space navigation are fully understood there will, from desire or necessity, come the idea of building a permanent home for men in space. The ease of actual navigation in space together with the difficulties of taking-off from or landing on planets like the earth with considerable gravitational fields will in the first place lead t o the necessity for bases for repairs and supplies not involving these difficulties. A damaged space vessel would, for instance, almost be bound to be destroyed in attempting earth landing. At first space navigators, and then scientists whose observations would be best conducted outside the earth, and then finally those who for any reason were dissatisfied with earthly conditions would come to inhabit these bases and found permanent spatial colonies. Even with our present primitive knowledge we can plan out such a celestial station in considerable detail.

Imagine a spherical shell ten miles or so in diameter, made of the lightest materials and mostly hollow; for this purpose the new molecular materials would be admirably suited. Owing to the absence of gravitation its construction would not be an engineering feat of any magnitude. The source of the material out of which this would be made would only be in small part drawn from the earth; for the great bulk of the structure would be made out of the substance of one or more smaller asteroids, rings of Saturn or other planetary detritus. The initial stages of construction are the most difficult to imagine. They will probably consist of attaching an asteroid of some hundred yards or so diameter to a space vessel, hollowing it out and using the removed material to build the first protective shell. Afterwards the shell could be re-worked, bit by bit, using elaborated and more suitable substances and at the same time increasing its size by diminishing its thickness. The globe would fulfil all the functions by which our earth manages to support life. In default of a gravitational field it has, perforce, to keep its atmosphere and the greater portion of its life inside; but as all its nourishment comes in the form of energy through its outer surface it would be forced to resemble on the whole an enormously complicated single-celled plant.

The outermost layer would have a protective and assimilative character. The presence of meteoric matter in the solar system moving at high speeds in eccentric orbits would be the most formidable danger in space travelling and space inhabitation. Certain meteorite swarms could be avoided altogether by keeping out of their tracks; larger meteorites could be detected at a distance by visual observation or by the effect of their gravitational fields. These might be avoided by changing the course of the globe or deflecting the meteorites by firing high-speed projectiles into them. Smaller meteorites would be impossible to avoid. The shell of the globe would have to be made strong enough not to be penetrated or cracked by them, and would have to possess regenerative mechanisms for repairing superficial damage. Possibly the function which our atmosphere performs for the earth could be imitated by jets of high-speed gas or electrons which, projected at meteorites, would vaporize them and thus prevent them d oing any damage. At the same time meteoric matter might be the chief source of the material required for the growth or propulsion of the globe if a method of assimilating it could be found.

The outer shell would be hard, transparent and thin. Its chief function would be to prevent the escape of gases from the interior, to preserve the rigidity of the structure, and to allow the free access of radiant energy. Immediately underneath this epidermis would be the apparatus for utilizing this energy either in the form of a network carrying a chlorophyll-like fluid capable of re-synthesizing carbohydrate bodies from carbon dioxide,. or some purely electrical contrivance for the absorption of radiant energy. In the latter case the globe would almost certainly be supplied with vast, tenuous, membranous wings which would increase its area of utilization of sunlight. The subcutaneous circulation would also have the necessary function of dissipating superfluous heat, in as low temperature radiation as possible. Underneath this layer would probably lie the main stores of the globe in the form of layers of solid oxygen, ice and carbon or hydro-carbons. Inside these layers, which might be a quarter o f a mile in thickness, would lie the controlling mechanisms of the globe. These mechanisms would primarily maintain the general metabolism, that is, they would regulate the atmosphere and climate both as to composition and movements. They would elaborate the necessary food products and distribute mechanical energy where it was required. They would also deal with all waste matters, reconverting them with the use of energy into a consumable form; for it must be remembered that the globe takes the place of the whole earth and not of any part of it, and in the earth nothing can afford to be permanently wasted. In this layer, too, would be the workshops and laboratories concerned with the improvement of the globe and arrangements for its growth.

Inside the mechanical layer would be the living region and here imagination has a more difficult task. It would, of course, not be necessary to have either houses or rooms in the same sense in which we have them on the earth. The absence of bad weather and of gravitation makes most of the uses that we have for houses superfluous. Perhaps we can safely assume that a certain number of cells closed by thin, but sound-proof, partitions would be necessary for work requiring special isolation, but the major part of the lives of the inhabitants of the globe would be spent in the free space which would occupy the greater portion of the center of the globe.

This three-dimensional, gravitationless way of living is very difficult for us to imagine, but there is no reason to suppose that we would not ultimately adjust ourselves to it. We should be released from the way we are dragged down on the surface of the earth all our lives: the slightest push against a relatively rigid object would send us yards away; a good jump - and we should be spinning across from one side of the globe to the other. Resistance to the air would, of course, come in, as it does on earth; but this could be turned to advantage by the use of short wings. Objects would become endowed with a peculiar levity. We should have to devise ways of holding them in place other than by putting them down; liquids and powders would at first cause great complications. An attempt to put down a cup of tea would result in the cup descending and the tea remaining as a vibrating globule in the air. Dust would be an unbearable nuisance and would have to be suppressed, because even wetting it would never make it settle. We should find in the end that all these things were great conveniences, but at first they would be extremely awkward. The possibilities of three-dimensional life would make the globes much roomier than their size would suggest. A globe interior eight miles across would contain as much effective space as a countryside one hundred and fifty miles square even if one gave a liberal allowance of air, say fifty feet above the ground.

The activity of the globe is, of course, by no means confined to its interior. In the first place it would necessarily have a number of effective sense and motor organs. Essentially the former would consist of an observatory which continually recorded the position of the globe and at the same time kept a look-out for an meteoric bodies of perceptible size which might damage it. On the whole the globe would not be designed for travel. It would move in an orbit around the sun without any expenditure of energy; but occasionally it might be necessary to shift its orbital position to a more advantageous one, and for this it would require a small motor of a rocket variety.

Yet the globe would be by no means isolated. It would be in continuous communication by wireless with other globes and with the earth, and this communication would include the transmission of every sort of sense message which we have at present acquired as well as those which we may require in the future. Interplanetary vessels would insure the transport of men and materials, and see to it that the colonies were not isolated units.

However, the essential positive activity of the globe or colony would be in the development, growth and reproduction of the globe. A globe which was merely a satisfactory way of continuing life indefinitely would barely be more than a reproduction of terrestrial conditions in a more restricted sphere. But the necessity of preserving the outer shell would prevent a continuous alteration of structure, and development would have to proceed either by the crustacean-like development in which a new and better globe could be put together inside the larger one, which could be subsequently broken open and re-absorbed; or, as in the molluscs, by the building out of new sections in a spiral form; or, more probably, by keeping the even simpler form of behavior of the protozoa by the building of a new globe outside the original globe, but in contact with it until it should be in a position to set up an independent existence.

So far we have considered the construction and mechanism of the globe rather than its inhabitants. The inhabitants can be divided into the personnel or the crew, and the citizens or passengers. With the first - except that their tasks would be more complicated and more scientific than those that fall to the officers and crew of a modern ship - we need not be concerned. To the others the globe would appear both as hotels and laboratories. The population of each globe would be by no means fixed; constant interchange would be taking place between them and the earth even when the greater portion of human beings were actually inhabiting globes. There would probably be no more need for government than in a modern hotel: there would be a few restrictions concerned with the safety of the vessel and that would be all.

Criticism might be made on the ground that life in a globe, say of twenty or thirty thousand inhabitants would be extremely dull, and that the diversity of scene, of animals and plants and historical associations which exist even in the smallest and most isolated country on earth would be lacking. This criticism is valid on the initial assumption that men have not in any way changed. Here, to make globe life plausible, we must anticipate the later chapters and assume men's interests and occupations to have altered. Already the scientist is more immersed in his work and concentrates more on relations with his colleagues than in the immediate life of his neighborhood. On the other hand, present æsthetic tendencies verge towards the abstract and do not demand so much inspiration from untouched nature. What has made a small town or a small country seem in the past a narrow sphere of interest has been on the one hand its isolation, and on the other hand the fact that the majority of its inhabitants are at so low a level of culture as to prevent any considerable intellectual interchange within its boundaries. Neither limitation holds for the globes, and the case of ancient Athens is enough to show that small size alone does not prevent cultural activity. Free communications and voluntary associations of interested persons will be the rule, and for those whose primary interest is in primitive nature there will always remain the earth which, free from the economic necessity of producing vast quantities of agricultural products, could be allowed to revert to a very much more natural state.

As the globes multiplied they would undoubtedly develop very differently according to their construction and to the tendencies of their colonists, and at the same time they would compete increasingly both for the sunlight which kept them alive and for the asteroidal and meteoric matter which enabled them to grow. Sooner or later this pressure, or perhaps the knowledge of the imminent failure of the sun, would force some more adventurous colony to set out beyond the bounds of the solar system. The difficulty involved in making this jump is probably as great as that of leaving the earth itself. Interstellar distances are so large that high velocities, approaching those of light, would be necessary; and though high velocities would be easy to attain - it being merely a matter of allowing acceleration to accumulate - they would expose the space vessels to very serious dangers, particularly from dispersed meteoric bodies. A space vessel would, in fact, have to be a comet, ejecting from its anterior end a s tream of gas which, meeting and vaporizing any matter in its path, would sweep it to the sides and behind in a luminous trail. Such a method would be very wasteful of matter, and one might perhaps count on some better one having been devised by that time. Even with such velocities journeys would have to last for hundreds and thousands of years, and it would be necessary - if man remains as he is - for colonies of ancestors to start out who might expect the arrival of remote descendants. This would require a self-sacrifice and a perfection of educational method that we could hardly demand at the present. However, once acclimatized to space living, it is unlikely that man will stop until he has roamed over and colonized most of the sidereal universe, or that even this will be the end. Man will not ultimately be content to be parasitic on the stars but will invade them and organize them for his own purposes.