[math-fun] Low-tech measurement of the wavelength of light

I once read about an experiment where you can measure the wavelength of light using a drop of oil and a pond. The idea is that the oil will disperse into a uniform film whose thickness (calculable as the volume of the drop divided by the surface area of the pond) is close to the frequency of visible light, and then you can observe chromatic effects. Can anyone provide a reference? I did a Google search but couldn't find the thing I recall reading. Thanks, Jim Propp