44 Common Science 



it by the force of adhesion. This is why your face gets 

 much dirtier when it is perspiring than when it is dry. 



Application 12. Explain why cobwebs do not fall from 

 the ceiling ; why dust clings to a wet broom ; why a postage 

 stamp does not fall off an envelope. 



Inference Exercise 

 Explain the following : 



41. There are no springs on the tops of high mountains. 



42. People used to shake sand over their letters after writing them 



in ink. 



43. People used to make night lights for bedrooms by pouring some 



oil into a cup of water and floating a piece of wick on the 

 oil. The oil always stayed on top of the water, and went 

 up through the wick fast enough to keep the light burning. 



44. Your face becomes much dirtier when you are perspiring. 



45. Ink bottles are usually made with wide bases. 



46. When you spill water on the floor, you cannot wipe it up with 



wrapping paper, but you can dry it easily with a cloth. 



47. Oiled mops are used in taking up dust. 



48. Cake will stick to a pan unless the pan is greased. 



49. Although the earth turns completely over every day, we never 



fall off it. 



50. Signs are fastened sometimes to windows or to the wind shields 



of automobiles by little rubber " suction caps." 



SECTION 8. The force that makes a thing hold together: 

 Cohesion. 



What makes rain fall in drops ? 

 Why are diamonds hard ? 



You have not yet touched any of the most dangerous 

 switches on the imaginary switchboard of universal 

 laws. But if your experience in turning off the capillary 

 attraction and adhesion switches did not discourage 

 you, you might try turning off the one beside them labeled 

 COHESION : 



