Molecular Attraction 41 



SECTION 7. How things stick to one another: Ad- 

 hesion. 



Why is it that when a thing is broken it will not stay to- 

 gether without glue ? 



Why does chalk stay on the blackboard ? 



Now that you have found out something about capil- 

 lary attraction, suppose that you should go to the imag- 

 inary switchboard again and tamper with some other 

 law of nature. An innocent-looking switch, right 

 above the capillary attraction switch, would be labeled 

 ADHESION. Suppose you have turned it off: 



In an instant the wall paper slips down from the 

 walls and crumples to a heap on the floor! The paint 

 and varnish drop from the woodwork like so much sand. 

 Every cobweb and speck of dust rolls off and falls in a 

 little black heap below. 



When you try to wash, you cannot wet your hands. 

 But they do not need washing, as the dirt tumbles off, 

 leaving them cleaner than they ever were before. You 

 can jump into a tank of water with all your clothes on 

 and come out as dry as you went in. You discover by 

 the dryness of your clothes that capillary attraction 

 stopped when the adhesion was turned off, for capillary 

 attraction is just a part of adhesion. But you are not 

 troubled now with the clamminess of unabsorbed per- 

 spiration. The perspiration rolls off in little drops, 

 not wetting anything but running to the ground like so 

 much quicksilver. 



Your hair is fluffier than after the most vigorous 

 shampoo. Your skin smarts with dryness. Your eyes 

 are almost blinded by their lack of tears. Even when 



