This prophecy of a noted economist is warranted: “Probably the greatest economic revolution which the youth of today may in his old age behold, will be found in this all-important branch of our industries.” When we know how nature works, we can adjust our little motions in time and place to promote that work; we shall have the art of moving things to suit our needs. Nothing can be truer than Tennyson’s line, “We rule by obeying nature’s powers.” Chapter II. Forces In Production Of Wealth. _Nature._—When men learn to meet their wants by exertion in accord with nature’s ways, they are said to use the forces of nature in production of wealth. Every accumulation of materials for satisfying future needs implies some control over natural objects. If advantage is taken of natural motions or other activities to bring about larger accumulation, the man whose plans secure this has gained control over, and so property-rights in, the natural force which he has harnessed. The wind caught by a sail and the water controlled by a dam contribute to the power, and indirectly to the wealth, of the man who contrives to make them move things for him. The directive actions of men necessarily appropriate the natural objects which they use, together with all the qualities of those objects. _Energy._—Human exertion produces wealth, as we have seen, whenever it anticipates and provides for future wants by securing at hand the things to be used. So far as this anticipation includes control of forces or qualities in nature, these natural agencies contribute to wealth of individuals or communities. So voluntary human exertion is combined with involuntary forces of outside nature to give wealth. No amount of gold in Alaska is wealth until some human ability has appropriated it to human uses; but the mere fact of locating a claim for mining purposes gives the prospector advantage over any other man because of his foresight. So every activity of nature may become a factor in wealth by human ingenuity in making it useful.