Wavelengths are frequently measured by passing parallel light waves perpendicular to the jet stream . Acting as a converging lens, each wave will project a pinpoint light onto a photographic plate situated at the focal
length. As the surface tension of the liquid jet changes because of surfac- taut diffusion to the air/liquid interface, each succeeding wave will have longer wavelength; i.e., will have lower surface tension values. It is obvi-
ous that flow rate of the jet will determine the surface age of each wave .