320 



PUMPS, AND THEIR VALUE TO MAN 



it not possible to rid the ship of the inflowing water by 

 strong pumps. 



Another and very different use to which pumps are put is 

 seen in the compression of gases. Air is forced into the tires 

 of bicycles and automobiles until they become sufficiently in- 

 flated to insure comfort in riding. Some present-day sys- 

 tems of artificial re- 

 frigeration could not 

 exist without the aid 

 of compressed gases. 



Compressed air has 



IffTK. WW played a very impor- 



K i&MBkt"'- tant role in mining, 



being sent into poorly 

 ventilated mines to 

 improve the condition 

 of the air, and to sup- 

 ply to the miners the 

 oxygen necessary for 

 respiration. Divers 

 and men who work 





FIG. 192. Carrying water home from the spring. 



under water carry on their backs a tank of compressed air, 

 and take from it the amount required. 



There are many forms of pumps. They serve widely different 

 purposes and are essential to the operation of many industrial 

 undertakings. 



The air as man's servant. Long before man harnessed 

 water for turbines, or steam for engines, he made the air serve 

 his purpose, and by means of it raised water from hidden 

 underground depths to the surface of the earth ; likewise, by 

 means of it, he raised to his dwelling on the hillside water 

 from the stream in the valley below. Those who live in cities 

 where running water is always present in the home cannot 



