But to make those narrow, ribbon-like, clean, long lines of rolled cotton, known as slivers, by machinery with greater precision and uniformity than is possible by hand, and with a thousand times greater rapidity, has been the work of many inventors at different times and in different countries. The machine cards are cylinders clothed with leather and provided with separate sets of slender, sharp, bent fingers. The different cards are arranged to move past each other in opposite directions, so as to catch and disentangle the fibres. Flat, overhead stationary cards are also used through which the cotton is carried. As one operation of carding is not sufficient for most purposes the cotton is subjected to one or more successive cardings. So ingenious is the structure in some of its parts that as the stream of cotton passes on, any existing knots do not fail to excite the attention of the machine, which at once arrests them and holds them until disentangled. In connection with the cards, combers and strippers are used to assist in further cleaning and straightening the fibre, which is finally removed from the cards and the combs by the doffer. The cotton is stripped from the doffer by the doffer knife and in the form of delicate, flat narrow ribbons, which are drawn through a small funnel to consolidate them, and finally delivered in a coiled form into a tall tin can. The material is then carried to a drawing frame, which takes the spongy slivers, and, carrying them through successive sets of rollers moving at increased speed, elongates, equalises, straightens and “doubles” them, and finally condenses them into two or more rolls by passing the same through a trumpet-shaped funnel. As the yarns still need to be twisted, they are passed through a roving frame similar to a drawing frame. An ingenious device connected with the winding of the roving yarns upon bobbins may be here noted. Formerly the bobbins on which the yarns were wound increased in speed as they were filled, thus endangering and often breaking the thread, and at all times increasing the tension. In 1823 Asa Arnold of Rhode Island invented “a differential motion” by which the velocity of the bobbin is kept uniform. The roving having been reduced to proper size for the intended number of yarns, now goes to the spinning machine, to still further draw out the threads and give to them a more uniform twist and tenuity. The spinning machine is simply an improved form of Crompton’s mule, already described.