CAPILLARITY. 



209 



liquid. If the solid body is moistened by the liquid, 

 the surface becomes curved upwards against the sides 

 of the solid it is concave ; if, on the contrary, the solid 

 is not moistened by the liquid, the liquid is depressed 

 against the sides of the solid the surface becomes convex. 



FIG. 148 (real size}. 



Fig. 148 A represents the surface of water in a vessel of 

 glass. Fig. 148 B represents the surface of mercury 

 in a vessel of glass. In tubes of which the internal 

 diameter is less than l cm , the whole surface of the liquid 

 becomes curved ; if such a tube is placed in a liquid 

 which wets it, the surface of the liquid in the tube will 

 be above the surface of the liquid outside. The ascent 

 of liquids in tubes is especially well marked if the bore 

 is very narrow, not larger than a hair (Lat. capillus) ; 

 such tubes are called capillary tubes, and the phenomena 

 themselves are investigated under the name capillarity. 

 If a tube is not moistened by the liquid in which it is 

 ' placed, the surface of the liquid within the tube will be 

 below that of the liquid outside. It is impossible to 

 enter here upon an explanation of these phenomena by 

 the action of molecular forces ; it will be sufficient to 

 describe some experiments on capillary phenomena. 



If several tubes of different internal diameters be 

 placed side by side in a liquid which wets them, 

 us shown in fig. 149, it will be seen that the liquid 

 stands higher when the tube is narrower, and that the 



