The spinning-mule consists of two principal portions: the first, which is fixed, contains the bobbins of rovings and the drawing rollers; the second is a sort of carriage, moving upon an iron railroad, and capable of being drawn out to a distance of about five feet from the fixed frame. This carriage carries the spindles, the number of which is half that of the bobbins of rovings. Motion is given to the spindles by means of vertical drums, round which are passed slender cords, communicating with the spindles. There is one drum to every twenty-four spindles. The carriage being run up to the point from which it starts in spinning, the spindles are near to the roller-beam; the rollers now begin to turn, and to give out yarn, which is immediately twisted by the revolution of the spindles; the carriage then moves away from the roller-beam, somewhat quicker than the threads are delivered, so that they receive a certain amount of stretching, which gives value to this machine. The beneficial effect is produced in this way,—when the thread leaves the rollers, it is thicker in some parts than in others, and those thicker parts not being so much twisted as the thinner ones are softer, and yield to the stretching power of the mule, so that the twist is equalised throughout, and the yarn becomes more uniform. When the carriage has _completed_ a _stretch_, or is drawn out from about fifty-four to sixty-four inches from the roller-beam, the drawing rollers cease to give out yarn, but the spindles continue to whirl until the threads are properly twisted. In spinning the finer yarns, the carriage sometimes makes what is called a _second stretch_, during which the spindles are made to revolve much more rapidly than before. The drawing, stretching, and twisting, of a length of thread being thus completed, the mule disengages itself from the parts of the machinery by which it has hitherto been driven, and the spinner then pushes the carriage with his knee back to the roller-beam, turning at the same time with his right hand a fly wheel, which gives motion to the spindles. At the same time a copping wire, as it is called, is pressed upon the threads by the spinners’ left hand, and they are thus made to traverse the whole length of the spindle, upon which they are then wound or _built_ in a conical form, which is called a _cop_. These cops are used for placing in the _shuttle_ in weaving, and form the weft or short cross threads of the cloth. [Illustration: Machinery for moving Shuttle. Shuttle for Power Loom.]