NOTE.—Several familiar examples of capillary attraction may be added. A piece of sponge, or a lump of sugar, touching water at its lowest corner, soon becomes moistened throughout. The wick of a lamp lifts the oil to supply the flame, to the height of several inches. A capillary glass tube, bent in the form of a syphon, and having its shorter end inserted in a vessel of water, will fill itself and deliver over the water in drops. A lock of thread or of candle-wick, inserted in a vessel of water in a similar manner, with one end hanging over the vessel, will exhibit the same result. An immense weight or mass may be raised through a small space, by first stretching a dry rope between it and a support, and then wetting the rope. The several figures above need no explanation to the attentive reader. FLOW OF WATER UNDER PRESSURE. Under this head three general cases are to be considered: 1, that of liquids _issuing from orifices_; 2, _their flow through tubes_, or in streams; and, 3, _the effects of the momentum and impact of liquids_. The principles governing the action of the two last will be introduced, 2, under that portion of the work relating to “piping,” and, 3, under the sections pertaining to the jet pump. Throughout the different portions of the book will the three cases be still further elucidated. Now, as to the laws governing the escape of liquids under pressure through an opening, it may be understood that when the liquid escapes from a vessel, owing to the excess of the internal pressure, _the volume which escapes depends on the section of the orifice and the velocity with which the liquid molecules move at the moment of their escape from it_. This velocity depends upon the density of the liquid, the excess of pressure at the opening, and the friction of the liquid, both at the opening and against the walls. When the aperture is made in a very thin wall of a large vessel, so as to remove, as much as possible, the causes tending to modify the motion of the escaping fluid, the laws of the escape are comprised in the following theorem, discovered by Torricelli, in 1643, as a consequence of the law of the fall of bodies discovered by Galileo: “Liquid molecules, flowing from an orifice, _have the same velocity, as if they fell freely in vacuo from a height equal to the vertical distance from the surface to the center of the orifice_.”