If a needle be dipped in certain liquids, a drop will remain suspended at its point when withdrawn from them: and, in general, when a solid body has been immersed in a liquid and withdrawn, it is _wet_; that is, some of the liquid has adhered to its surfaces. If no attraction existed between the solid and liquid, the solid would be in the same state after immersion as before. This is proved by liquids and solids between which no attraction exists. If a piece of glass be immersed in mercury, it will be in the same state when withdrawn as before it was immersed. No mercury will adhere to it; it will not be _wet_. When it rains, the person and vesture are affected only because this attraction exists between them and water. If it rained mercury, none would adhere to them. (101.) When molecular attraction is exhibited by liquids pervading the interstices of porous bodies, ascending in crevices or in the bores of small tubes, it is called _capillary attraction_. Instances of this are innumerable. Liquids are thus drawn into the pores of sponge, sugar, lamp-wick, &c. The animal and vegetable kingdom furnish numerous examples of this class of effects. A weight being suspended by a dry rope, will be drawn upwards through a considerable height, if the rope be moistened with a wet sponge. The attraction of the particles composing the rope for the water is in this case so powerful, that the tension produced by several hundred weight cannot expel them. A glass tube, of small bore, being dipped in water tinged by mixture with a little ink, will retain a quantity of the liquid suspended when withdrawn. The height of the liquid in the tube will be seen by looking through it. It is found that the less the bore of the tube is, the greater will be the height of the column sustained. A series of such tubes fixed in the same frame, with their lower orifices at the same level, and with bores gradually decreasing, being dipped in the liquid, will exhibit columns gradually increasing. A _capillary syphon_ is formed of a hank of cotton threads, one end of which is immersed in the vessel containing the liquid, and the other is carried into the vessel into which the liquid is to be transferred. The liquid may be thus drawn from the one vessel into the other. The same effect may be produced by a glass syphon with a small bore. (102.) It frequently happens that a _molecular repulsion_ is exhibited between a solid and a liquid. If a piece of wood be immersed in quicksilver, the liquid will be depressed at that part of the surface which is near the wood; and in like manner, if it be contained in a glass vessel, it will be depressed at the edges. In a barometer tube, the surface of the mercury is convex, owing partly to the repulsion between the glass and mercury.