The space .distributions of vorticity were measured by using a vorticimctcr (vorti-city probe) in the field induced by a vortex shedding from the wing-tip of a rectangular wing under different angles of attack. The results show that the vorticimetcr having the advantages of high sensitivity, simpler calibration process and easiness to use, is capable of measuring the vorticity directly, and finding out the center trace of the vortex core exactly. Through the measurements, a counter rotating vortex with a center strength of 1/17 to that of the main wing-tip vortex existing nearby is discovered. The center vorticity would decay substantially as the main wing-tip vertex moves down-stream. For instance, the peak vorticity at x = 2.5c (c, the chord length) will decay to about 25% of that at x = 0.1c, while its scale remains almost unchanged. At the cross-section x = 0.1c, the scale of the wing-tip vortex was about 0.2c spanwisc and-0.18c along the longtudinal direction. Finally, the strengths of a pair of
