Rayleigh (1878) examined a common experience: a thin jet of liquid is unstable and breaks into droplets. When a jet is thin enough, the effect of gravity is negligible compared to surface energy. The jet changes its shape to reduce the total surface energy. Liquid flow sets the time.

Similar instability in solids. Phenomena similar to the Rayleigh instability occur in solid state; see Rodel and Glaeser (1990) for an experimental demonstration and for a literature survey. For example, at a high temperature, a penny-shaped pore in a solid first blunts its edge, from which finger-like tunnels emerge, and the tunnels then break into small cavities (Lange and Clarke 1982).