1. IN A DEVICE FOR LIFTING INDETERMINATE WEIGHTS, MEANS FOR CAUSING OPERATION OF THE DEVICE IN A WEIGHT-LIFTING DIRECTION, AN ELECTRICAL CIRCUIT FOR CONTROLLING SUCH OPERATION, SPRING MEANS, OPERATIVELY CONNECTED TO SAID DEVICE AND DEFLECTABLE IN RESPONSE TO THE WEIGHT IMPOSED ON SAID DEVICE, SWITCH MEANS IN SAID CIRCUIT OPERATIVE IN RESPONSE TO DEFLECTION OF SAID SPRING MEANS BY A WEIGHT GREATER THAN A PREDETERMINED MAXIMUM TO PREVENT OPERATION OF THE LIFTING DEVICE IN A WEIGHT-LIFTING DIRECTION, AND MEANS MAINTAINING SAID SWITCH IN OPERATION-PREVENTING CONDITION UNTIL REDUCTION OF THE DEFLECTION OF THE SPRING MEANS CORRESPONDING TO REDUCTION OF THE IMPOSED WEIGHT TO A PREDETERMINED VALUE BELOW THE PREDETERMINED MAXIMUM.