 Oscillation at intermediate Strouhal numbers is characterized by the buildup and rapidly subsequent shedding of vortices.For spheres in uniform flow in the Reynolds number range of 8×102 < Re < 2×105 there co-exist two values of the Strouhal number.The lower frequency is attributed to the large-scale instability of the wake, is independent of the Reynolds number Re and is approximately equal to 0.2.