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I am writing in response to an article in the July 28 issue, “Having gathered moss, water drops roll.” You should have taken the time to find out that Lycopodium is not a moss. It’s true that a common name for the plant is club moss, but Lycopodium is in the division Lycophyta, sometimes called seedless vascular plants or fern allies. Ann E. Rushing
Baylor University
Waco, Texas
You report inaccurately that water droplets normally “dribble like tears down a slanting surface.” Close observation will show that every solo trickle of water in fact has a well-defined spherical head. It’s quick and easy to miss, but definitely observable. Because it usually leaves a trail as it rolls down the surface, a solo trickle may seem to be tear-shaped, but actual tear-shaped drops are only the ones that have not broken the grip of surface tension adhesion. Other easily observed “liquid marbles” are found almost any time you turn a water hose on the top of a car, especially if the spray is backlit by the sun. You almost always see a profusion of little spheres bouncing and scattering without adhesion over the wet surface. Phil Henshaw
New York, N.Y.