Switch Engine at Night   The firefly dance of the switchmen talking with light:   Vertical lanternstreak printed on darkness vivid, imperative: "kick" sign. The engineer widens the throttle, wheels spin, sand spurts under them, crash of couplers as slack runs out cars lurch into motion.   Sharp, swift arc of a lantern: stop sign. Gloved hand smacks brake valve, sand valve and throttle, howl of diesel subsides, air hisses, one worn brake shoe screams.   Cut-off boxcars black elephants trunk to tail in the darkness walk quietly down a siding. Slow, stupid, blind, they bump tusk into rump into a line of their brothers: the crash echoes.   More lanternchalk on the blackboard of night: this time a circle. The engine backs off, grumbling and clanking. The lanterns climb onto the footboards, each dragging a switchman. Paul J. Sampson   Paul J. Sampson (pauljsampson@yahoo.com) still regrets leaving his job as a locomotive fireman on the Rock Island Line.