[From the Encyclopaedia Britannica.] 



LXXXIII. Capillary Action. 



A TUBE, the bore of which is so small that it will only admit a hair 

 (capilla), is called a capillary tube. When such a tube of glass, open at both 

 ends, is placed vertically with its lower end immersed in water, the water is 

 observed to rise in the tube, and to stand within the tube at a higher level 

 than the water outside. The action between the capillary tube and the water 

 has been called Capillary Action, and the name has been extended to many 

 other phenomena which have been found to depend on properties of liquids 

 and solids similar to those which cause water to rise in capillary tubes. 



The forces which are concerned in these phenomena are those which act 

 between neighbouring parts of the same substance, and which are called forces 

 of cohesion, and those which act between portions of matter of different kinds, 

 which are called forces of adhesion. These forces are quite insensible between 

 two portions of matter separated by any distance which we can directly measure. 

 It is only when the distance becomes exceedingly small that these forces be- 

 come perceptible. Quincke* has made experiments to determine the greatest 

 distance at which the effect of these forces is sensible, and he finds for various 

 substances distances about the twenty-thousandth part of a millimetre. 



Poggendorfft tells us that Leonardo da Vinci J must be considered as the 

 discoverer of capillary phenomena. 



The first accurate observations of the capillary action of tubes and glass 

 plates were made by Hauksbee. He ascribes the action to an attraction be- 

 tween the glass and the liquid. He observed that the effect was the same in 

 thick tubes as in thin, and concluded that only those particles of the glass 

 which are very near the surface have any influence on the phenomenon. 



* Fogg. Ann., cxxxvn. p. 402. t Fogg. Ann., ci. p. 551. J Died 1519. 



Physico- Mechanical Experiments, London, 1709, pp. 139169; and Phil. Trans., 1711 and 1712. 



