"When a filled pen is held point downwards, the ink it contains is acted on by a variety of forces, among which may be reckoned gravity, inertia, capillary attraction, air pressure, friction, and the viscosity of the liquid, as well as several minor forces. If the pen is properly made, these forces are in a state of equilibrium, and the ink does not run out of the reservoir. As soon, however, as the point touches a surface it is capable of wetting, the action of the capillary attraction is altered, with the result that the ink is enabled to flow from the reservoir, and that the pen writes."