Molecular Attraction 



39 



FIG. 20. The water rises through the lamp wick by capillary attraction. 



The space between the threads of the wick, and espe- 

 cially the still finer spaces between the fibers that make 

 up the threads, act like fine tubes and the liquid rises 

 in them just as it did in the fine glass tube. Wherever 

 there are fine spaces between the particles of anything, 

 as there are in a lump of sugar, a towel, a blotter, a wick, 

 and hundreds of other things, these spaces act like fine 

 tubes and the liquid goes into them. The force that 

 causes the liquid to move along fine tubes or openings 

 is called capillary attraction. 



Capillary attraction this tendency of liquids to go 

 into fine tubes is caused by the same force that makes 

 things cling to each other (adhesion), and that makes 

 things hold together (cohesion) . The next two sections tell 

 about these two forces ; so you will understand the cause 



