It cannot be denied that our elementary discussions of the principal phenomena connected with surface tension and capillarity are often vague and unsatisfying. The simple statics of the systems dealt with are frequently obscured and circumvented by the introduction of the concept of free surface energy to replace surface tension. The lecture is an attempt to clarify some of the points which arise from this failure to come to grips with fundamentals.

On the basis of the usual idea of cohesion between molecules it can be shown, for instance, that, in contradiction to what is often contended, it is not necessary to deny the reality of surface tension during the course of an explanation of the common phenomena which were, at one time, regarded as providing evidence of its existence. It is possible, also, to gain a less abstract conception of the distinction between free and total surface energy than that provided by a purely thermodynamical discussion.

The customary assumption that in a system containing a solid/liquid interface the surface energy of the solid plays an identical rôle with that of the liquid is criticized, and the conception of surface energy as the work done during the rupture of a column of material is examined. Capillarv elevation is regarded as a consequence of negative surface tension in the liquid at the solid/liquid interface, and the usual expression for the capillary rise is derived from this idea.