And how did Arkwright effect this great revolution? He asked himself whether it was not possible, instead of a wheel which spins a single thread of cotton at a time, and by means of which the spinner could obtain in twenty-four hours about two ounces of thread,--whether it might not be possible to spin the same material upon a great number of wheels, from which many hundreds of threads might issue at the same moment. The difficulty was in giving to these numerous wheels, spinning so many threads, the peculiar action of two hands when they pinch, at a little distance from each other, a lock of cotton, rendering it finer as it is drawn out. It was necessary, also, at the same time, to imitate the action of the spindle, which twisted together the filaments at the moment they had attained the necessary degree of fineness. It would be extremely difficult, if not impossible, to give an adequate idea, by words, of the complex machinery by which Arkwright accomplished his object. Since Arkwright's time prodigious improvements have been made in the machinery for cotton-spinning; but the principle remains the same, namely, to enable rollers to do the work of human fingers, with much greater precision, and incomparably cheaper. We will attempt briefly to describe this chief portion of the great invention. We must suppose that, by the previous operation of carding, the cotton-wool has been so combed and prepared as to be formed into a long untwisted line of about the thickness of a man's finger. This line so formed (after it has been introduced into the spinning-machine) is called a _roving_, the old name in hand-spinning. [Illustration: Arkwright's original spinning-machine.]