3. A GYROSCOPE COMPRISING, MEANS FOR PRODUCING A UNIDIRECTIONAL MAGNETIC FIELD HAVING A SELECTED DIRECTION, A SINGLE SAMPLE OF FLUID MATERIAL CONTAINING TWO SELECTED KINDS OF ATOMIC NUCLEI POSITIONED IN SAID MAGNETIC FIELD, MEANS FOR PRODUCING A PAIR OF NUCLEAR MAGNETIC RESONANCE SIGNALS FROM SAID NUCLEI, EACH NUCLEAR MAGNETIC RESONANCE SIGNAL HAVING A FREQUENCY NOMINALLY EQUAL TO THE LARMOR FREQUENCY OF THE KIND OF NUCLEI FROM WHICH IT IS DERIVED, A FIRST OSCILLATION GENERATOR PRODUCING A FIRST OUTPUT SIGNAL HAVING A FREQUENCY SUBSTANTIALLY EQUAL TO THE LARMOR FREQUENCY OF ONE OF SAID KINDS OF NUCLEI, A SECOND OSCILLATION GENERATOR PRODUCING A SECOND OUTPUT SIGNAL HAVING A FREQUENCY SUBSTANTIALLY EQUAL TO THE LARMOR FREQUENCY OF THE OTHER OF SAID KINDS OF NUCLEI, FEEDBACK LOOP MEANS FOR BRINGING THE FREQUENCIES OF SAID OUTPUT SIGNALS AND THE FREQUENCIES OF RESPECTIVE ONES OF SAID PAIR OF NUCLEAR MAGNETIC RESONANCE SIGNALS INTO EQUALITY, AND MEANS COMPARING THE PHASES OF SAID FIRST AND SECOND OCCILLATION GENERATORS TO PRODUCE A SYSTEM OUTPUT SIGNAL PROPORTIONAL TO THE PHASE DIFFERENCE THEREOF.