SCIENCE OF COMMON THINGS. 99 



Common suction-pump. Height water rises in common pump. 



the other. Its structure is such, that, while the 

 pressure of fluid on one side has a tendency to close 

 it, the pressure on the other side has a tendency to 

 open it. 



/tys. 21, 22, and 23 represent the various forms of valves used in 

 pumps, water-engines, etc. 



Fig. at. Fig. 22. Fig. 53. 



637 How can water be raised by the common suction-pump ? 



As the action of this pump depends upon the pressure 

 of the atmosphere, water cannot be raised by it from a 

 depth of more than 34 feet below the upper valve, and 

 in practice a much shorter limit is usually assigned. 



633 A tinman of Seville, in Spain, ignorant of the principles of science, 

 undertook to construct a suction-pump to raise water from a well sixty feet 

 deep ; when the machine was finished, he was confounded at discovering 

 that it had no power to raise water at all, and enraged at his disappoint- 

 ment, while some one was working the pump, he struck the suction pipe with 

 a hammer or axe so forcibly as to crack it, when, to his surprise and delight, 

 the water almost immediately began to flow, and he found he had attained 

 his purpose. How is this result to be accounted for ? 



The explanation is as follows : the air pressed in 

 through the slit, or aperture of the suction-pipe, and 

 becoming mixed with the water in its ascent, formed a 

 compound fluid far lighter than water alone, and there- 

 fore acted upon more readily by the atmospheric pres- 

 sure ; and thus produced the phenomenon described. 



639 How high can water be raised in the suction-pump by resorting t* 

 Hie expedient above described ? 



About fifty-five feet, instead of thirty to thirty-four. 



6*1O To whom is the invention oftJie common pump attributed ? 



To Ctesibius, an Athenian engineer, who lived at 

 Alexandria, in Egypt, about the middle of the second 

 century before the Christian era. 



