Surface Tension — Rayleigh–Plateau A smooth stream of water always falls apart into drops. Surface tension wants the least possible skin: fattening one spot and pinching another shrinks the surface, so any ripple longer than the jet’s circumference runs away and the thread snaps. The journey: Plateau (1849) measured the cut-off; Rayleigh (1878) turned it into a growth rate with Bessel functions, fastest at wavelength ≈ 9.0 × the radius. Slide the ripple below one circumference and the jet just wobbles — it never breaks.