1. V. On the formation of vortex rings by drops falling into liquids, and some allied phenomena
2. The present work relates to changes in surface tension due to surfactant monolayers, and how these changes affect drop induced vortex formation. One of the conclusions of Thomson and Newall (Ref. 2) was that the absence of surface tension promotes the formation of vortex rings. Careful reading of their work reveals that their reference to surface tension does not refer to the surface tension between the liquid and the air, but rather the surface tension between the vortex ring fluid and the bulk fluid, which is zero when the drop fluid and bulk fluid are the same, as is the case in the present study.
3. Formation of vortex rings from falling drops
4. We note in passing that drops falling at velocities approaching terminal velocity will oscillate about a nonspherical drop shape (Refs. 6 and 7). The velocities for drops falling from the low drop heights considered here are much less than terminal velocity and should, therefore, oscillate about an approximately spherical shape.