The guide comb is of interesting construction. It is capable of expansion or contraction. Each tooth of the comb projects from an iron box, and is kept in position by being passed through the coils of several spiral springs; by means of a screw and nut at each end these springs can be compressed, thus diminishing the distance between the comb-teeth equally at all parts of the comb. When the expanding combs are used, far leveller beams are made than are otherwise attainable. In the event of a thread breaking, the warper must have some arrangement for running the yarn back, so as to find the broken end to piece it up. This is obtained by six falling rods placed above seven fixed ones. When the machine is running forward the sheet of yarn passes between the fixed and loose rods, the latter resting on a slide. When the machine is reversed, the slide receives a slight impulse, allowing one rod to drop, say 3-1/2 feet, the yarn being suspended at the top by the fixed rods; whilst this rod is dropping it pushes the slide still further, and another drops, and so on, until when the sixth rod has fallen, twelve times 3-1/2 feet equalling 42 feet of yarn are taken up. This is ample for piecing purposes; indeed, the woman in attendance seldom finds it necessary to go so far. [Illustration: FIG. 10. FIG. 11. PLATE II. _To face pp. 26 and 27._] Prevention, however, is better than cure, and several machines are on the market fitted with stop motions to arrest the action of the machine at the breakage of a single end, and reducing the number of falling rods to two. One favourite system is to have a small bent wire, not unlike a hairpin, but about 1-1/4 inch in length, suspended from each thread and held in position by slots across the frame. This system is shown in Plate II., Figs. 10 and 11. Immediately under these pins are two nip rollers M (Fig. 10), revolving in contact, one of them borne on a movable centre, and attached to an upright lever N. This is immediately above an upright slide I, the bottom of which is connected to one end of a lever centred on the drum shaft of the frame. At the other end of the lever is a foot board and also the connection of a long rod with heavy balance weight always tending to press the footboard up, and consequently the slide down. The machine is driven by a single open strap on the pulley, which, however, does not actuate the machine until it is pressed against the friction plate.