1. AN ATOMIC RESONANCE APPARATUS INCLUDING, MEANS FOR PRODUCING AN ASSEMBLAGE OF ATMOIC PARTICLES, MEANS FOR SUBJECTING SAID ASSEMBLAGE OF ATOMIC PARTICLES TO AN ALTERNATING MAGNETIC FIELD FOR PRODUCING ATOMIC RESONANCE OF SAID ATOMIC PARTICLES, MEANS FOR PRODUCING AND SUBJECTING SAID ASSEMBLAGE OF ATOMIC PARTICLES TO A POLARIZING MAGNETIC FIELD FOR ALIGNING SAID RESONANT ATOMIC PARTICLES, MEANS FOR SHIELDING SAID ASSEMBLAGE OF RESONANT ATOMIC PARTICLES FOR EXTRANEOUSLY PRODUCED MAGNETIC FIELDS, SAID SHIELDING MEANS INCLUDING A MAGNETICALLY PERMEABLE STRUCTURE ENCOMPASSING SAID ASSEMBLAGE OF RESONANT ATOMIC PARTICLES AND HAVING A PAIR OF DIAMETRICALLY OPPOSED MAGNETICALLY PERMEABLE END WALL PORTIONS, AND SAID POLARIZING MAGNETIC FIELD PRODUCING MEANS INCLUDING AN ELECTRICAL COIL WOUND INSIDE OF SAID SHIELD MEANS INBETWEEN SAID DIAMETRICALLY OPPOSED MAGNETICALLY PERMEABLE END WALL PORTIONS, SAID COIL HAVING AN AXIAL EXTENT SUBTENDING SUBSTANTIALLY THE FULL LENGTH OF THE SPACE BETWEEN SAID OPPOSED END WALL PORTIONS WHEREBY UNDESIRED END EFFECT PERTURBATIONS OF THE POLARIZING MAGNETIC FIELD WITHIN SAID SHIELD MEANS ARE MINIMIZED.