The spinning-mule, invented by Samuel Crompton, carried the mechanism of the cotton-factory many steps in advance. Long after Crompton, came the self-acting mule. It is a carriage some twenty or thirty feet long, travelling to and fro, and drawing out the most delicate threads through hundreds of spindles, whirling at a rate which scarcely permits the eye to trace their motion. Mr. Whitworth says,--"So great are the improvements effected in spinning machinery, that one man can attend to a mule containing 1088 spindles, each spinning 3 hanks, or 3264 hanks in the aggregate per day. In Hindustan, where they still spin by hand, it would be extravagant to expect a spinner to accomplish one hank per day; so that in the United States [and in Great Britain also] we find the same amount of manual labour, by improved machinery, doing more than 3000 times the work." [Illustration: Samuel Crompton, inventor of the spinning-mule.] Of the rapidity with which some portions of the machinery operate, we may form an idea from the fact that the very finest thread which is used in making lace is passed through the strong flame of a lamp, which burns off the fibres without burning the thread itself. The velocity with which the thread moves is so great, that we cannot perceive any motion at all. The line of thread, passing off a wheel through the flame, looks as if were perfectly at rest; and it appears a miracle that it is not burnt. [Illustration: Cotton Mule-spinning.] The invention of Arkwright--the substitution of rollers for fingers--changed the commerce of the world. The machinery by which a man, or woman, or even child, could produce two hundred threads where one was produced before, caused a cheapness of production much greater than that of India, where human labour is scarcely worth anything. But the fabric of cotton was also infinitely improved by the machinery. The hand of the spinner was unequal to its operations. It sometimes produced a fine thread, and sometimes a coarse one; and therefore the quality of the cloth could not be relied upon. The yarn which is spun by machinery is sorted with the greatest exactness, and numbered according to its quality. This circumstance alone, which could only result from machinery, has a direct tendency to diminish the cost of production. Machinery not only adds to human power, and economizes human time, but it works up the most common materials into articles of value, and equalizes the use of valuable materials. Thus, in linen of which the thread is spun by the hand, a thick thread and a thin thread will be found side by side; and, therefore, not only is material wasted, but the fabric is less durable, because it wears unequally.