Consider the free body diagram of a surface element of a water - glass meniscus in a vacuum. Along the line normal to the surface, the water pressure acts towards the vacuum, and the direction of the surface tension 'curvature force' depends on whether the surface curves like a 'u' or like an 'n'. In the case of water, the curve is a 'u', so the curvature force acts in the same direction as the water pressure force. Which force, acting towards the water along the normal to the surface, balances these? I was trying to figure out the profile curve of the meniscus, but stumbled quite early on! I can just about convince myself why the curve should be 'u' shaped by thinking about energy minimisation, but when I associate each energy with a force (gravitational p.e. - water pressure; surface energy - surface tension) I can't get over this issue. Unless the meniscus is in fact 'n' shaped in a vacuum, and the atmospheric pressure is the 'mystery' force.