A Dictionary of Music and Musicians/Tracker
TRACKER. A thin flat strip of wood used in the mechanism of an organ for the purpose of conveying leverage from one portion of the instrument to another. A tracker differs from a sticker in the fact that a tracker pulls, while a sticker pushes; while therefore a tracker can be flat and thin, a sticker is round and rigid. For example, if, when one end of a key is pressed down it raises a sticker at its other end, it is clear that the sticker will push up a lever at a higher level; but the other end of the lever at the higher level will of course descend, and to this therefore must be attached a tracker. It will be evident also that a sticker, having only to remain in an upright position, can be kept in its place simply by means of a bit of wire inserted at each end and passing loosely through holes in the ends of the levers. But a tracker having to pull and be pulled is provided at each end with a tap-wire (or wire like a screw) which when passed through the hole in the lever is secured by a leather button. In all cases noisy action is prevented by the insertion of a layer of cloth or some other soft material. Trackers are generally made of pine-wood about one eighth of an inch in thickness and from one third to a half of an inch in width. The length of trackers varies of course according to circumstances; in long 'actions' or extended 'movements' (as for example, when mechanism is taken under a floor or up a wall) they are sometimes twelve or more feet in length; in such cases they are formed of two or more parts joined together by wire. In order to prevent long trackers from swinging about laterally when in use they are often made to pass through a register or thin board containing holes of suitable size lined with cloth. A tracker may convey leverage from any part of an instrument to another, but its final function is to lower the pull-down and let air pass through the pallet into the pipe.
[ J. S. ]