The instability of an annular thread of fluid

The instability of an annular coating of liquid on a wire or on the inside of a small tube subject to capillary forces at its free surface is discussed. It was found that for given values of s/a, the ratio of the two radii of the annulus, and S ≡ρTa/μ2, the reciprocal of the square of the Ohnesorge number, there is a disturbance of a certain wavelength (2πa/λ)*, which grows more rapidly than disturbances of any other wavelength. One would therefore expect the liquid to break up into a regular pattern of drops with spacing given by this wavelength. The dependence of (2πa/λ)* on s/a and S has been calculated and is presented graphically. Experimental observations on drop formation on wires and in tubes which agree with the calculations are given.