1. A SPRING-OPERATED SOURCE OF CONSTANT TORQUE COMPRISING, IN COMBINATION: (A) A BARREL MEMBER HAVING A AXIS: (D) A SHAFT MEMBER MOUNTED ON SAID BARREL MEMBER FOR ROTATION ABOUT SAID AXIS; (C) A SPIRAL SPRING OPERATIVELY INTERPOSED BETWEEN SAID MEMBERS FOR WINDING AND UNWINDING THEREOF AND FOR CORRESPONDING CHANGES IN THE STRESS OF SAID SPRING WHEN SAID MEMBERS ROTATE RELATIVE TO EACH OTHER; (D) A DRIVING WHEEL; (E) MEANS FOR ROTATING SAID WHEEL IN A PREDTERMINED DIRECTION; (F) CLUTCH MEANS NORMALLY RESPONSIVE TO ROTATION OF SAID DRIVING WHEEL IN SAID DIRECTION FOR DRIVINGLY CONNECTING THE SAME TO ONE OF SAID MEMBERS AND FOR THEREBY THE SAME TO ONE OF SAID MEMBERS AND FOR (G) CLUTCH CONTROL MEANS OPERATIVE TO DISENGAGE SAID CLUTCH MEANS IN RESPONSE TO A PREDETERMINED MINIMUM STRESS OF SAID SPRING WHILE SAID DRIVING WHEEL IS ROTATED IN SAID DIRECITON, AND TO LOCK THE OTHER ONE OF SAID MEMBERS TO SAID DRIVING WHEEL IN RESPONSE TO RELATIVE ROTATION OF SAID MEMBERS UNDER THE DRIVING FORCE OF SAID SPRING THROUGH A NUMBER OF REVOLUTIONS GREATER THAN ONE, WHEN SAID DRIVING WHEEL STANDS STILL.