There have been vast numbers of patents taken out for wave-motors. One was invented in Chili, South America, which furnished a constant power for four months, and was utilized in sawing planks. The action of waves is more constant on the Pacific coast of America than elsewhere, and some auxiliary power, such as a gasoline engine, which can be quickly started and stopped, must be provided for use during calm days. The prime cost of such a machine need not exceed that of a steam plant, and the cost of operating is much less than that of any fuel-burning engine. The saving of coal is a very important problem. In a wider sense, we may say that the saving of all the great stores which nature has laid up for us during the past, and which have remained almost untouched until the nineteenth century, is _the_ great problem of to-day. Petroleum and natural gas may disappear. The ores of gold, silver, and platinum will not last forever. Trees will grow, and iron ores seem to be practically inexhaustible. Chemistry has added a new metal in aluminum, which replaces copper for many purposes. One of the greatest problems of the twentieth century is to discover some chemical process for treating iron, by which oxidation will not take place. Coal, next to grain, is the most important of nature’s gifts; it can be exhausted, or the cost of mining it become so great that it cannot be obtained in the countries where it is most needed; water, wind, and wave power may take its place to a limited extent, and greater use may be made of the waste gases coming from blast or smelter furnaces, but as nearly all energy comes from coal, its use must be economized, and the greatest economy will come from pulverizing coal and using it in the shape of a fine powder. Inventions have been made trying to deliver this powder into the fire-box as fast as made, for it is as explosive as gunpowder, and as dangerous to store or handle. If this can be done, there will be a saving of coal due to perfect and smokeless combustion, as the admission of air can be entirely regulated, the same blast which throws in the powder furnishing oxygen. Some investigators have estimated that the saving of coal will be as great as twenty per cent. This means 100,000,000 tons of coal annually. Bituminous coal will then be as smokeless as anthracite, and can be burned in locomotives. Cities will be free from the nuisance of wasted coal, which we call soot. This process will be the best kind of mechanical stoking, and will prevent the necessity of opening the doors of fire-boxes. The boiler-rooms of steamships will no longer be “floating hells,” and the firing of large locomotives will become easy.