58 LIVING IN AN OCEAN OF AIR 



spheres, about two feet in diameter, were placed together, 

 making a hollow ball, and the air was pumped out of 

 them. The atmosphere held these two hemispheres to- 

 gether so tightly that eight horses on each side were 

 unable to pull the hemispheres apart. 



Importance of Atmospheric Pressure. The common 

 uses of atmospheric pressure are varied and numerous. 

 From the act of breathing to the measurement of the 

 height of mountains there are thousands of ways in which 

 man makes use of atmospheric pressure. It assists in 

 the pumping of water. The barometer tells how high air- 

 craft rise, and assists in foretelling weather. Variations 

 in atmospheric pressure make our winds and storms and 

 cause droughts and floods. The success of farmers' crops 

 or of curing foodstuffs in the open may depend upon atmos- 

 pheric pressure. In the development of life from the 

 beginning, animals and plants on the earth have been 

 accustomed to a certain atmospheric pressure, as can be 

 seen when deep-sea fish are rapidly brought to the surface. 

 Such fish sometimes actually explode when they are drawn 

 suddenly to the surface of the water, where atmospheric 

 pressure is much less than that to which they are accus- 

 tomed. People who go to the tops of very high mountains 

 fail to get enough oxygen, and the decrease in air pressure 

 causes bleeding from blood vessels which break under the 

 lessened pressure. 



SELF-TESTING EXERCISE 



Select from the following list of words those which best fill the blank 

 spaces in the sentences below and arrange the words in proper numerical 

 order. A word may be used more than once. 



weight Aristotle water space 



support vacuum push speed 



height pounds pressure Torricelli 



sea atmospheric weather mercury 



ounces square height mountain 



cubic force vacant Galileo 



