Dobbies are occasionally of single lift, but in the cotton trade far more frequently double. The difference is in the double lift having two sets of knives: either knife can lift any heald, and, by duplicating, a second knife can be preparing for and even commencing to lift a heald as the first drops; it thus saves time and increases speed. In single lift machines only one knife is used, and in case of a heald having to be raised two picks in succession, it would have to be dropped to the bottom of the shed after the first pick, and raised again. A double lift Keighley is often called, in error, a single lift, in consequence of only one shedding rod being used; it however lifts twice in one complete stroke. Dobbies have the advantage over tappets in increased power of weaving fancier cloths, a greater number of picks to the round, and a possibility of changing to other patterns. [Illustration: FIG. A. FIG. B. FIG. C. PLATE VII. _To face pp. 104 and 105._] The leading characteristic of dobbies is, that by means of pegs placed in revolving lattices, any heald can be selected and raised by the machine. The favourite dobby is the improved Keighley, first patented in 1867 by Messrs. Hattersley & Smith, of that town--it was used to a considerable extent, but recent improvements have greatly increased its value. Plate VII. and Fig. 48 show a general view of the machine--one of Henry Livesey’s, Limited, make, on Ward’s principle, 20 jacks, double lift. At the under side is seen a pegged lattice; immediately above the pegs and resting on the topmost lag is a row of levers, double the number of shafts or jacks representing the capacity. The [T] knife lever works on the centre shown, and slides the knives backwards and forwards in grooves at A and B. The jacks to which at one end the heald cords are attached have at the other end latches fixed to them, which are out of the way of the sliding knives, unless purposely dropped on to them. When a lag is in gear without any pegs, none of the latches touch the knives, and there is consequently no raising of the healds. If all the holes be pegged, one end of each lever is raised, the other end depressed, and consequently all the latches drop on the knives; at the next stroke of which all the healds will be lifted. By pegging a few of the holes, say the 1st, 3rd, and 10th, we should find only those three healds lifted; in this manner any desired working of the healds may be obtained. The lattice is made up of lags, each of which suffices for two picks, and as the barrel of the dobby will not hold less than 8 lags, a pattern of 16 picks or more is required, unless a smaller pattern be repeated. In pegging, the lags are placed so that the lattice stands as in the machine, thus:-- [Illustration: FIG. 49. Numbers 1 to 10 indicate the picks; L 1 to L 5 indicate the lags.]