Magnetic field strength measuring devices

Claim 1

IN A DEVICE FOR MEASURING MAGNETIC FIELD STRENGTH BY THE HALL EFFECT, A THIN PROBE STRUCTURE HAVING AN EXTENDED BRIDGE-SHAPED STRATUM OF BISMUTH AT MOST ABOUT 0.001 INCH THICH, WHICH STATUM HAS TWO TRANSVERSELY EXTENDING CROSSING BRIDGE AXES EACH OF SUBSTANTIAL LENGTH, SAID STRATUM HAVING ONE PAIR OF BRIDGE TERMINALS AT THE OPPOSITE END REGIONS OF ONE OF SAID TWO AXES, AND A FURTHER PAIR OF BRIDGE TERMINALS AT THE OPPOSITE END REGIONS OF THE OTHER OF SAID TWO AXES, A BRIDGE CIRCUIT CONNECTED TO SAID TWO PAIRS OF TERMINALS INCLUDING AN ALTERNATING CURRENT SUPPLY CIRCUIT AND CONNECTIONS FROM SAID SUPPLY CIRCUIT TO SAID ONE PAIR OF TERMINALS FOR CAUSING PREDETERMINED ALTERNATING CURRENT TO FLOW THROUGH SAID STRATUM IN THE GENERAL DIRECTION OF SAID ONE AXIS, SAID BRIDGE CIRCUIT ALSO INCLUDING AN ALTERNATING CURRENT OUTPUT CIRCUIT CONNECTED TO SAID FURTHER PAIR OF TERMINALS OF SAID STRATUM, SAID BRIDGE CIRCUIT ALSO INCLUDING BALANCING CIRCUIT ELEMENTS FOR RESISTIVELY AND INDUCTIVELY BALANCING SAID BRIDGE CIRCUIT SAID DETERMINING MEANS OPERATIVE IN RESPONSE TO THE ALTERNATING CURRENT FLOWING IN THE OUTPUT CIRCUIT OF THE BALANCED BRIDGE CIRCUIT FOR CAUSING SAID OUTPUT CIRCUIT TO GIVE A PREDETERMINED INDICATION WHEN SAID STRATUM IS EXPOSED TO A MAGNETIC FIELD OF A PREDETERMINED STRENGTH.