but of substance itself in general; for what were we to do when by the increase of human bodies all the earth's substance had been absorbed? Were we to prey upon the other orbs of space, and thus increase our earth into unknown future dimensions? Some pretended already, even in the reality of this twenty-ninth century, to decipher that prospect upon the future horizon. Already, it might be said, we were, at times and in places, hard run to maintain the full needed supplies, the carbon and oxygen, nitrogen and hydrogen, and the other lesser needs, being kept unremittingly at work in their successive coursing through our material frames. In this growing relative scarcity, one body must perhaps imbibe at once what another throws off. The laboratory intervenes to convert exhaled poison into indispensable nutriment. The ubiquitous reign of chemistry is already triumphant.
Returning to the dream, one vast field of business seemed opening out, in providing from time to time the extensions to our atmosphere, as required, on the one hand, by extension of subterranean excavation, and, on the other, by the overcrowding aerial population. When the volume of our wants in oxygen and nitrogen had become too great for the slow and costly process of decomposing the earth's solid masses, we had recourse to outside supplies, and had already made considerable havoc of Jupiter's gaseous envelope, where both the gases in question were to be had unlimitedly for the taking, only that the expense of disengaging and deporting was very considerable. But latterly the grand source of the most suitable and most economical supply had been the comets.
