MeniscusNo. 133
Surface tension · made visible

The skin on water Water climbs a bank of narrow glass tubes — the finer the bore, the higher it rises — held up by an invisible elastic skin.

Tap a tube · watch the column ring & settle

Water is reluctant to have a surface.

Every drop is wrapped in a skin one molecule thick — cohesion pulling each molecule inward, so the liquid holds the smallest possible face to the air. Push a fine glass tube into water and that skin does something strange: it climbs. The glass tugs on the water harder than the water tugs on itself, and the column crawls upward until its own weight balances the pull. Narrow the bore and it climbs higher still.
Jurin's law

Halve the bore, double the rise

Height rises in exact inverse to the tube's radius. A half-millimetre bore lifts water near thirty millimetres; open the bore to a full millimetre and the climb falls by half. The bank reads the law directly — the thinnest tubes stand tallest.

h = 2γ·cosθ / (ρ·g·r)  ·  h ∝ 1/r
The meniscus

A surface that curves to the wall

Because glass wets, water is highest where it touches the wall and lowest in the middle — a concave dish. That curvature is the skin under tension, and the tighter the bore the deeper the dish. The bright line along each top is light catching the taut surface.

contact angle θ ≈ 0° on clean glass
Coalescence

Two drops become one, at once

Let a bead grow at the rim and the moment it touches the column the skin cannot hold two surfaces — they snap into one in under a millisecond, and the shock rings the whole column. Tap the glass yourself and you set the same oscillation going.

merge time ~ 10⁻³ s · then damped ringing