In a woolen mule the spools of sliver are placed in a fixed frame, and the sliver passes between a pair of rollers to the spindles. These stand, slightly inclined backwards, in a long row upon the movable carriage. At first the spindle tips are close to the rollers. The sliver is paid out, and at the same time the carriage bearing the revolving spindles retreats. During this time no yarn is wound on the bobbins, but the slivers are being twisted. Then the rollers cease to pay out sliver, the carriage moves out a little further, and the spindles rotate faster, so that the yarn is being twisted and stretched. When sufficient twist has been imparted the carriage moves back again and the spindles wind up the twisted yarn on to the bobbins. This, briefly, is the operation of the mule. There are a great many intricate devices in this machine which deserve attention, but which hardly fall within our scope. All that remains now is to wind the yarn on spools, or skein it, before it is ready for the weaver. 2. THE MANUFACTURE OF WOOLEN CLOTH [Sidenote: _Weaving_] There are many differences between weaving worsteds and woolens, but for our purposes we may consider the process the same, as in a general way it is. Some cloths are woven with a cotton warp and a woolen yarn filling, the warp being carefully concealed. Woolen cloths are more frequently woven with a backing than worsteds. This means that either there is a double warp, a double weft, or both. The object of backing is usually to add strength and warmth to the material, and the lower side is therefore often woven of coarser yarn. In some cases, however, notably in travelling rugs, the backing may be just as elaborate as the face, and this necessitates a rather intricate mounting process. [Sidenote: _Carpets_] Carpet weaving is one of the large branches of the woolen industry, and for this purpose the coarsest and longest fibred wools (common, braid, and carpet wools) are usually employed. These wools readily lend themselves to the manufacture of a coarse thick yarn, which in turn produces a thick, durable material. The thickness of a carpet is known as the pile. [Sidenote: _Finishing Important in Woolens_]