“Yes they will. Sheep will not be required for their wool any more than their flesh. A substitute will be found for leather as well as beef. Better and more durable clothing will be made directly from minerals than were produced in your time from vegetable and animal substances. Metals and artificial mineral products began early in the twentieth century and even before, to supplant wood in buildings and many other structures. So at present the use of wood is greatly reduced and during the coming century it will be almost discontinued; a great many things are now made of Alumina that were formerly made of wood, and that metal has become cheaper and more abundant than iron. Glass is also very much used, and methods have been discovered of giving it any desired temper, so that it is made flexible and tough like pewter or firm and elastic like steel. It can also be made fibrous and soft as cotton and can be spun and woven into textile fabrics.” “But what are they going to do for power and fuel?” I asked. “If there is to be such an increase of population, an enormous consumption of fuel and power will follow. Of course they will use the coal while it lasts, but the supply of that limited, and if that is the only dependence, all industries will sooner or later be brought to an end.” “The coal,” said he, “was an excellent makeshift for temporary use until a more enduring supply of power was discovered to supersede it. But even now it could if necessary be almost entirely dispensed with and yet there are still vast deposits of it untouched. In the long distant future the time will come when the coal will be regarded as a deposit of food for your race as it is now with ours, but it will not be consumed for its heat or its power except in that way.” “Have our people then learned how to get power as you do from the use of the principle of the repulsion of gravitation?”