It will be seen that we contemplate a time when man’s will shall be law to the physical world, and he shall no longer be deterred by such abstractions as time and space, height and depth, weight and hardness, but shall indeed be the lord of creation. “Well,” says the faithless reader, “ ‘life is short, but art is long;’ where is the power that will effect all these changes?” This it is the very object of Mr. Etzler’s volume to show. At present, he would merely remind us that there are innumerable and immeasurable powers already existing in nature, unimproved on a large scale, or for generous and universal ends, amply sufficient for these purposes. He would only indicate their existence, as a surveyor makes known the existence of a water-power on any stream; but for their application he refers us to a sequel to this book, called the “Mechanical System.” A few of the most obvious and familiar of these powers are the Wind, the Tide, the Waves, the Sunshine. Let us consider their value. First, there is the power of the Wind, constantly exerted over the globe. It appears from observation of a sailing-vessel, and from scientific tables, that the average power of the wind is equal to that of one horse for every one hundred square feet. “We know,” says our author— “that ships of the first class carry sails two hundred feet high; we may, therefore, equally, on land, oppose to the wind surfaces of the same height. Imagine a line of such surfaces one mile, or about 5,000 feet, long; they would then contain 1,000,000 square feet. Let these surfaces intersect the direction of the wind at right angles, by some contrivance, and receive, consequently, its full power at all times. Its average power being equal to one horse for every 100 square feet, the total power would be equal to 1,000,000 divided by 100, or 10,000 horses’ power. Allowing the power of one horse to equal that of ten men, the power of 10,000 horses is equal to 100,000 men. But as men cannot work uninterruptedly, but want about half the time for sleep and repose, the same power would be equal to 200,000 men.... We are not limited to the height of 200 feet; we might extend, if required, the application of this power to the height of the clouds, by means of kites.” But we will have one such fence for every square mile of the globe’s surface, for, as the wind usually strikes the earth at an angle of more than two degrees, which is evident from observing its effect on the high sea, it admits of even a closer approach. As the surface of the globe contains about 200,000,000 square miles, the whole power of the wind on these surfaces would equal 40,000,000,000,000 men’s power, and “would perform 80,000 times as much work as all the men on earth could effect with their nerves.”