Consider the situation depicted in Fig. 1.1, in which the end of a capillary tube of radius, r, is immersed in a liquid. For sufficiently small capillaries, one observes a substantial rise of liquid to height, h, in the capillary, because of the force exerted on the liquid due to surface tension. Equilibrium occurs when the force of gravity on the volume of liquid balances the force due to surface tension. The balance point can be used to measure the surface tension: