1. IN AN ARRANGEMENT OF THE CHARACTER DESCRIBED, IN COMBINATION, SWITCH MEANS HAVING A PAIR OF CONTACT MEANS MOVABLE BETWEEN AN OPEN AND A CLOSED POSITION AND CONSTRUCTED TO NORMALLY STAY IN ONE OF SAID POSITIONS AND TO MOVE TO THE OTHER OF SAID POSITIONS THEREOF WHEN SUBJECTED TO A MAGNETIC FIELD; SUPPORT MEANS SUPPORTING SAID SWITCH MEANS; AND AN ELECTROMAGNET HAVING AN ARMATURE MOVABLE IN A GIVEN DIRECTION FROM A REST POSITION TO AN ACTIVE POSITION UPON ENERGIZING THE ELECTROMAGNET, AND A MEMBER OF SOFT IRON ON SAID ARMATURE ARRANGED SO THAT AT LEAST PART OF THE MAGNETIC FIELD PRODUCED DURING ENERGIZING SAID ELECTROMAGNET PASSES THROUGH SAID MEMBER OF SOFT IRON TO MAGNETIZE THE LATTER, SAID ARMATURE AND SAID SOFT IRON MEMBER THEREON ARRANGED RELATIVE TO SAID SWITCH MEANS IN SUCH A MANNER THAT UPON ENERGIZING OF SAID ELECTROMAGNET AND MOVEMENT OF SAID ARMATURE FROM SAID REST TO SAID ACTIVE POSITION AT LEAST PART OF THE MAGNETIC FIELD PRODUCED IN SAID SOFT IRON MEMBER ACTS, WHEN SAID ARMATURE IS IN SAID ACTIVE POSITION, ON SAID SWITCH MEANS TO MOVE THE LATTER FROM SAID ONE TO THE OTHER POSITION THEREOF.