For changing the shuttle a drop-box loom is generally employed. In a double drop-box machine six boxes may be used at each side of the loom, any one of which may be brought into action, giving a scope of eleven colours of weft. The single drop box is, however, more usually employed, with four or six boxes at one side of the loom, only giving four or six colours, but not allowing less than two picks of the same colour to be put in. To insert single picks of colour a double-box loom is used, and possesses a special pick-and-pick arrangement (uncommon in the cotton trade) to admit of its picking twice consecutively from either side of the loom. The number of boxes just mentioned is seldom met with in the cotton trade, three and four boxes being the usual sizes. The single four-shuttle drop box carries a frame at one end of the slay in which the boxes or shelves rise or fall. These boxes contain the shuttles, and by suitable regulating motions the boxes may be shifted so as to bring any one shuttle level with the shuttle race and in front of the picker. The spindle is duplicated, and the couple is placed in front of the box, not above, as in a plain over-pick loom. The picker is broad and is without nib, fixed in a horizontal position, so as to act on any one of the shuttles which may be placed before it. The principal drop-box regulating motions are Diggle’s chain and Wright Shaw’s motion. DIGGLE’S CHAIN MOTION. Diggle’s chain is noted for short patterns, is simple in construction, and sure in its action. Attached to the loom top is a star wheel A and barrel B revolving on a stud. The barrel carries a chain C, of different sizes of links united by pins; the star wheel receives its motion through a train of wheels from the crank-shaft, of which D and E are connections. The links of the chain support a lever F, connected with another lever G at the loom side supporting the drop boxes. For a four-shuttle box the links are of four heights, the deepest raising the boxes to the highest point, while the lowest link supports the levers so that the boxes are at the bottom, with the top shuttle level with the shuttle race. The chain is arranged so that a sufficient number of links of the same height are placed together where several picks of the same colour are required. The shapes of the links are varied to adapt the lifts from or sinking to different boxes--thus, for a four-box loom twenty different shapes of links may be used to give lifts or depressions from any box of the four to any other; their arrangement in chain depends on the before-mentioned principle. A plate of links is shown at Fig. 72. They will be seen to be of four different heights. A 44-inch loom of this make may run 150 picks per minute. The change of shuttle is made immediately the shuttle enters the box. We are not able to change the shuttle at less intervals than two picks, but can do so at greater intervals--say, for example, once in four picks. [Illustration: FIG. 71.]