(from *Capillus*, hair), resembling a hair, fine, minute, small in diameter though long.

**CAPILLARY ACTION.**

1. When a solid body is partially plunged in a fluid, the level surface near it is disturbed, and the fluid is observed either to ascend or descend, so as to form a ring round the part immersed. If a tube of glass be inserted in a vessel containing water, the liquid will rise in a concave ring, both on the outside and the inside; and if the tube be small enough, the cylinder of water within it will be elevated above the general level, and the elevation will be greater nearly in the same proportion that the bore is less. On the other hand, if the tube be plunged in mercury, the fluid in contact with the glass will be depressed, forming a hollow ring with the convexity upward; and when the diameter is very small, the cylinder of mercury in the inside will sink below the level on the outside. In all these appearances the physical cause is the same, and it has received the name of Capillary Action, because its effects are most remarkable in the case of tubes with extremely minute diameters.

No part of natural philosophy has been the subject of a greater variety of researches than capillary action. It has been viewed in almost every possible light, and it would be difficult to suggest a new principle that has not been proposed by some philosopher in order to account for the observed appearances. One advantage has resulted from repeated discussion; for by this means the true cause of the phenomena is no longer doubtful, although there is still considerable difference of opinion with regard to the manner in which the effects are produced. It is now universally allowed, that the suspension of fluids in capillary tubes is to be ascribed to the attraction observed to take place between the elementary particles of which bodies are composed. We shall not stop to detail the different experiments which prove the reality of this attractive force, and we shall at once assume that the two following facts, which are the fundamental principles of this theory, are fully established; namely, that glass and other solid bodies attract the particles of fluids with which they are in contact, and that the particles of fluids attract one another. Admitting these two kinds of attraction, it remains to investigate the consequences that flow from them.

2. Corpuscular attraction acts with great intensity in Law of contact, or at the nearest distances, but it decreases very corpuscular rapidly as the distance increases, and, on the whole, is con-attraction, fixed within a very small range. Clairaut supposed that the sides of a capillary tube extend their action to the central parts of the contained cylinder of fluid. But in this opinion he is singular. All other philosophers confine the sphere of attraction within much narrower limits. They suppose that the corpuscular force has produced its full effect, and has become evanescent, at a distance so small that it cannot be appreciated by the senses. But