In order both to strengthen the warp threads and to make them smoother for weaving it is usual to apply some starchy or glutinous substance to them. This operation, which is performed in a machine called the Slasher, is termed yarn sizing, and consists of running the threads through a bath of preparation and then drying them quickly on a large steam-filled drum or can. One slasher will do enough work for 200 to 500 looms. [Illustration: _The Slasher_] [Sidenote: _Healding_] Since it is necessary that the warp threads may be lowered or raised in various combinations to allow the passage of the shuttle, each warp thread must be passed through an eye in the centre of a harness wire. Where, for instance, the warp is to be raised and depressed in three even sections there will be three harness frames, each fitted with enough heald-wires to accommodate one-third of the number of threads in the entire warp. In the Jacquard loom, used for intricate patterns, each warp-thread is separately controlled. The passing of the ends of the warp through their proper harness wires is a delicate and skilfull operation known as healding, or drawing-in. At the same time that this is done the threads are passed through individual stop-motion wires, relaxed tension on any one of which will bring the loom to a stop. [Illustration: _Drawing In_] [Sidenote: _Reeding_] Closely connected with drawing-in, is the final step in the preparation of the warp, and this is called reeding or sleying. In order to keep the warp threads in proper position during weaving they are passed through the wires of what looks like a comb with a strip across the open ends. This, the sley or reed, is attached to the batten on the loom and serves in addition to drive home each weft thread after the shuttle has passed. [Sidenote: _Warp Tieing_] When the loom has devoured all the warp threads contained on one beam, all that is necessary, if the pattern is to be continued, is to tie the ends of the old warp to the ends of the new, and this is accomplished with marvelous accuracy by a little machine built on the same principle as the Barber Knotter. This avoids drawing-in a second time. [Illustration: _Weaving Shed of Power Looms_] [Sidenote: _The Power Loom_]