CAPILLARY ATTRACTION and RE PULSION. If a tube of very small diameter be plunged into a fluid, the fluid in the tube eithet rises above or sinks below the level of that on the exterior, and at the same time is slightly curved at its upper surface. In cases where the fluid stands higher within the tube than without, as is the case With water and glass, its upper surface is always concave; but when the fluid is loWer within the tube, as with mercury and glass, it is convex. These phenomena are the resulti of what are termed capillary attraction and repulsion.
The laws according to which a fluid thus rises or falls are as follow :-1. When a tube of dry glass is plunged in a vessel of water, the attraction of the glass does not extend be yond the depth of the very thin film of water which would adhere to the interior surface if the tube were drawn out. 2. If the tube pre viously moistened by such film were plunged in water, the rise would be much less than in the other case ; and, whatever be the substance of the tube so moistened, the elevation of the water in it is found to be the same. 3. When cylindrical tubes of different diameters are compared, the elevation is inversely propor tional to tho diameter. 4. If the interior of
the tube be conical, the elevation or depression in it is found to depend on the diameter at the upper part only of the elevation; and to be the same as in a cylindrical tube of that diameter. 5. If the tube be double (one tube within another), the fluid rises to the same height in the interval between the two tubes, as it would do in a tube with that interval for its radius. 6. Between two parallel plates immersed at a very small interval, the fluid rises as high as in a tube with that interval for its radius. 7. Between two plates vertically placed, but inclined at every small angle (like a double screen nearly closed), the fluid rises higher and higher as we proceed towards the upright line of junction ; and the curve of the upper surface of the fluid is an hyperbola.
As an example of capillary action exempli fying itself in every-day processes, we may mention the rick of a candle or lamp, in which oil or melted tallow rises solely by virtue of this power.