For we shall certainly not have failed to act upon our knowledge of the fact that irregularities in the proportion of atmospheric moisture are responsible for the unhealthiness of certain areas; and we shall have learned, by means of the anhydrator, to provide any place with exactly the degree of damp or dryness necessary to health. The same apparatus, by desiccating the air to the extreme point, will keep the houses of an ocean city dry and thus do away with an objection which would make homes built on the water insufferable to-day. If we have not wholly reformed throughout the world our system of land tenure, the conquered ocean will unquestionably relieve the tension which is created by it, and perhaps a radical change of this character will only become possible when the enormous advantages of it have been practically exemplified. But there is another way in which the conquest of ocean ought to prove a great economic boon to the world. Except in the case of a few coal mines, with shafts sunk near the sea beach, we have hardly at all begun to investigate the contents of the ocean floor. There is, so far as I am aware, no particular reason to doubt that the constitution of the subterranean world is in most respects very much the same under the sea as under the land. Probably vast riches, as yet undreamed of, lie below the surface of the ocean and beneath its floor. There can be no question that the needs of the world will make us eager to tap them, as we should already have begun to, if any way could be discovered of overcoming the engineering difficulties involved. These difficulties, in the present state of our knowledge, may well appal the stoutest imagination. The problem presented by the immense and paralysing air pressure in a mine at this great depth would have to be overcome. Even in some great terrestrial excavations already made the problem occurs: and where (as in river tunnels and elsewhere) men attempt to work in great air-pressures artificially induced, the phenomenon called caisson-disease occasions practical difficulty. But the mere fact of an achievement being almost inconceivable in the light of present knowledge and invention must not be allowed to put a clog upon a forecast of what next century may attain. It is a hypothesis which the reader has been invited to accept, not merely that discovery and invention will go on, but that they will go at a constantly-increasing pace. We must not, therefore, allow what may well seem, at the present day, insuperable engineering difficulties to forbid the belief that the undiscovered wealth of the earth below the sea will be tapped for the benefit of the new age. What minerals may lie there, a rich heirloom for the coming time, we can but roughly imagine. But enterprise and the world's necessities will spur us on to search them out, until the new people, deriving like a fresh Antæus constant stores of strength from Mother Earth, will enter into possessions