Surface Tension. 



Fle ' 



actlon ol 



throughout the liquid and is very strong; but only the 



molecules at the surface show 



its influence because it is only 



these which are not pulled 



evenly in all directions by water 



molecules on every side, thus 



leaving the interior ones free to 



move in any direction, while 



those on the surface are only 



pu"lled toward the sides and to- 



ward the interior. In Fig. 3 is 



illustrated one method of show- 



ing the action of surface ten- 



sion. Here the dry camel's 



hair brush at the left shows the 



individual hairs standing apart, and when the brush is 



placed in the water they still stand apart, but when it is 



removed, as shown on the right, the whole are closely com- 



pacted by the pull of the surface film. 



50. Rise of Water in Capillary Tubes. It is surface ten- 

 sion which causes the rise of water in capillary tubes, as 

 represented in Fig. 4, above the level of the water in the 

 open vessel in which they are placed, when the water wets 

 the glass tube that is when the attraction of the glass for 

 the water is stronger than the attraction of the water, as 

 explained in (191) and (192). The 

 rows of molecules of glass just above 

 the water level attract and lift the 

 water closest to them but, as these 

 are moved upward, they draw after 

 themselves more water also. This 

 attraction is felt over a distance 

 which Quinke estimates at not far 

 from mnTTHT of an inch. The first 

 lifting of the water by the glass 

 brings it near enough to other glass 



PIG. 4. Rise of water ia cap- , & , n j , , 



niary tubes. molecules next above and the water 



is drawn still higher; in this way 

 3 



