CAPILLARY ACTION. 



251 



be wetted by the water. For the same reason water contained in 

 a narrow vessel of about J to \ inch internal diameter will have a 

 concave surface ; whilst mercury in a similar vessel will have a 

 convex surface. A rise of the liquid 

 inside a narrow tube will similarly be 

 observed on dipping it into water, the 

 amount of ascent being the greater 

 the narrower the tube (fig. 102) ; 

 whilst if dipped into mercury, the 

 quicksilver will stand at a lower level 

 inside the tube than outside, the 

 difference of level, as before, being 

 greater the narrower the tube. Ob- 

 tain two flat plates of glass and tie 

 them side by side together, with a 

 thin strip of cardboard or glassbetween 

 them at one side, so that the space en- 

 closed between them is wedge-shaped. 

 Place the plates in a vessel of water, 

 and a rise upwards of the fluid will Fig. 102. Capillary Tubes and 

 be observed between the plates, Water : a, b, c, d, height of 



greatest at the narrow end of the Water, 

 wedge, and least at the wider end, so as to trace out a curve. 

 If placed in mercury an analogous sunken curve, due to depression, 



Fig. 103. U Tube containing Fig.' 104. U Tube containing 



Mercury. Water. 



will result, less easy to see on account of the opacity of the 

 mercury. 



Expt. 296. Capillary Action in Narrow Tubes. Get a piece 

 of glass tubing some 6 inches long and J to J inch bore ; draw 

 it out in a lamp flame or gas jet (Expt. 48), and whilst hot bend 

 it up into a U shape (fig. 103), so that one limb of the U is 



