THE REASON WHY. 143 



" The wind bloweth where it listeth, and thou hearest the sound thereof, but 



canst not tell whence it cometh, and whither it goeth : so is every one 



that is born of the Spirit." JOHIT II., in. 



downward movement, to prevent the water from rushing back' 

 again. 



652. Hoiv high will atmospheric pressure raise water in 

 the bore of a pump ? 



It will raise water to an elevation of thirty feet above its level. 



653. W hy will it raise water to an elevation of thirty- 

 feet? 



Because a column of water ef thirty feet high, nearly balances the 

 weight of a column of air of equal surface, extending to tJit whole 

 height of the atmosphere. When, therefore, water is elevated to the 

 height of thirty feet, the power of the pump is enfeebled, as the air 

 and the water balance each other. 



654. How is water raised to a greater elevation when it is 

 required ? 



By mechanical contrivances, by which the water is forced to a 

 greater elevation. 



655. Why does water run through the "bent tube called a 

 typhon ? 



Because the atmospheric pressure upon the water on the outside 

 of the syphon forces it into the tube as fast as the syphon empties 

 itself through its longer arm. 



656. Why does water run through the longer arm of the 

 syphon ? 



Because the weight of the water in the longer arm of the syphon 

 is greater than that in the shorter ; therefore it runs out by its 

 own gravity. And, as in running out, it creates a tendency 

 towards a vacuum, the pressure of the outer air comes into 

 operation, and forces the water through the tube. 



657. Why does water issue from the earth in springs? 

 Some springs are caused by natural syphon* formed in the 



fissures of rocks, which, communicating with bodies of water, are 

 continually filled by atmospheric pressure, and therefore convey 

 streams of water to the point where they are set free. 



