The actual spinning and twisting operations being thus completed, the yarns are ready to be combined either for more elaborate types of twist, or for the processes of cloth manufacture. In its simplest definition, a fabric consists of two series of threads interlaced in such way as to form a more or less solid and compact structure. The two series of threads which are interlaced receive the technical terms of warp and weft--in poetical language, warp and woof. The threads which form the length of the cloth constitute the warp, while the transverse threads are the weft. The warp threads have ultimately to be wound or "beamed" on to a large roller, termed a weaver's beam, while the weft yarn has to be prepared in suitable shape for the shuttle. These two distinct conditions necessitate two general types of winding: (_a_) Spool winding or bobbin winding for the warp yarns. (_b_) Cop winding or pirn winding for the weft yarns. For the jute trade, the bulk of the warp yarn is wound from the spinning bobbin on to large rolls or spools which contain from 7 to 8 lb. of yarn; the weft is wound from the spinning bobbin into cops which weigh approximately 4 to 8 ounces. Originally all jute yarns for warp were wound on to flanged bobbins very similar to, but larger than, those which are at present used for the linen trade. The advent of the roll-winding machine marked a great advance in the method of winding warp yarns as compared with the bobbin winding method; indeed, in the jute trade, the latter are used only for winding from hank those yarns which have been bleached, dyed or similarly treated. Fig. 22 illustrates one of the modern bobbin winding machines for jute made by Messrs. Charles Parker, Sons & Co., Dundee. The finished product is illustrated by two full bobbins on the stand and close to a single empty bobbin. There are also two full bobbins in the winding position, and several hanks of yarn on the swifts. Each bobbin is driven by means of two discs, and since the drive is by surface contact between the discs and the bobbin, an almost constant speed is imparted to the yarn throughout the process. An automatic stop motion is provided for each bobbin; this apparatus lifts the bobbin clear of the discs when the bobbin is filled as exemplified in the illustration. The distance between the flanges of the bobbin is, obviously, a fixed one in any one machine, and the diameter over the yarn is limited. On the other hand, rolls may be made of varying widths and any suitable diameter. And while a bobbin holds about 2 lb. of yarn, a common size of roll weighs, as already stated, from 7 to 8 lb. Such a roll measures, about 9 in. long and 8 in. diameter; hence for 8 lb. yarn, the roll capacity is 14,400 yards.