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OBSERVATION OF QUANTIZED CIRCULATION IN SUPERFLUID HELIUM Circulation of the superfluid component of liquid-helium II around a fine wire has been measured by means of the influence that the circulation exerts on the transverse vibrations of the wire. The work is a repetition and extension of an experiment performed earlier by Vinen. It gives new evidence in support of the Onsager-Feynman hypothesis that circulation of superfluid helium is quantized in units of h/m, where h is Planck's constant and m is the mass of the helium atom. A fine wire is stretched down the center of a cylindrical vessel containing liquid helium, and the circulation is prepared by rotating the vessel around the axis of the wire while cooling from above T. Then the rotation of the vessel is stopped, and A. the wire is set into vibration by passing a current pulse through it in the presence of a transverse magnetic field. The free, slowly damped vibrations which follow can then be observed by means of the oscillatory e.m.f. induced along the wire. If circulation exists around the wire its influence on a cylindrically symmetric wire is to cause the plane of vibration of the wire to precess at a rate proportional to the circulation, in the same direction as the circulation. As the plane of 1. W. F. Vinen, Proc. Roy. Soc. (London) A260, 218 (1961). CONTENTS LIST OF FIGURES LIST OF TABLES I. INTRODUCTION A. The Two-Fluid Model B. Superfluid Flow C. The Vinen Experiment vii 19. Number of Observations vs Apparent Circulation for Runs C-l and C-4. Time in Stable Levels vs Apparent Circulation for Run C-4 20. Number of Observations vs Apparent Circulation for Runs D-l and D-6. Time in Stable Levels vs Apparent Circulation for Runs D-l and D-6 21. Time in Stable Levels vs Apparent Circulation for Run D-4 22. Time in Stable Levels vs Apparent Circulation for Run E-l 23. Time in Stable Levels vs Apparent Circulation for Runs E-3 and E-5 24. Time in Stable Levels vs Apparent Circulation for Run E-6 25. Time in Stable Levels vs Apparent Circulation for Run E-7 132 26. Time in Stable Levels vs Apparent Circulation for Run H-2 133 27. Au> vs P s /p, for Wire E 28. Signal Amplitude as a Function of Time with Normal Modes Excited Unequally vii LIST OF TABLES Experimental Parameters for Runs with Wire C. .. 112 Experimental Parameters for Runs with Wire D. . .