‘Coriolis Con Men’ Have Times Readers in a Swirl

Last week’s Q & A stated that the Coriolis force--caused by the Earth’s rotation, deflecting a moving body to the right in the Northern Hemisphere and to the left in the Southern--would affect the rotational direction of draining water only in large bodies, such as ponds, lakes and reservoirs. Many Times readers have written to Science File in rebuttal, saying that they visited the equator and were shown water in small basins circling in opposite directions just a few yards north and south of the equator. Unfortunately, those people have witnessed only a little sleight of hand by “Coriolis con men,” says astronomer Neil de Grasse Tyson, head of the Hayden Planetarium. It is very easy to control the rotation of the water by tilting the bowl slightly, he said, by blowing gently on the surface or by other techniques. The Coriolis force, he added, is simply “swamped” by a very large number of local forces. “I hope those people weren’t paying money for the demonstrations,” he added.