=330. Advantages of machines.=—Practically, however, the great extension in the use of machinery has depended on the power obtained from coal through steam. Only in the period since the adoption of improved forms of steam-engine have we realized the possibilities of machines. They can be applied only to certain classes of work, especially that involving the constant repetition of an operation which can be easily regulated either by the machine itself or by a laborer supervising it. We can use machines, for instance, to make cloth and even to make clothes, but we do not use them in the operations of dressing and undressing. In their proper field, however, they are indispensable. They will accomplish tasks which are too great or too small for human hands. They repeat a process or copy a model with absolute fidelity. They never grow tired and they have no human failings; they often economize time and materials. Finally, and this is the point of decisive importance, in many lines of work they, furnish the product at a cost far below that of hand labor. =331. Revolution in old industries effected by machinery.=—To describe the manifold applications of machinery in the nineteenth century, within the limits of this manual, is impossible. Let the reader glance from the book to the objects surrounding him, and make a list of the ten objects which first attract his attention. If he will trace their history he will find, in all probability, that they are all the products of complicated machinery, which has been developed from the simplest beginnings in the course of the century. He will probably experience difficulty in finding a familiar object which has not been subjected to machine processes unknown in 1800. Machinery has heightened human productivity in certain lines a hundred or even a thousand fold. At the Atlanta Cotton Exposition of 1881, two carders, two spinners, and one weaver, from the mountain region of Georgia, could produce eight yards of coarse cotton cloth in a day of ten hours. The same number of persons in a modern cotton factory could produce 800 yards by machinery. The cotton goods produced for home consumption in the United States by 160,000 laborers at that time, would have required the services of 16,000,000 laborers without machinery. Again, a skilful woman can knit 80 stitches a minute by hand; a machine enables her to make 480,000.