66 



ELEMENTARY SCIENCE 



large as ab, and ab be forced down one inch, then AB will 

 be forced up one- tenth of an inch. The pressure at A B is 

 ten times as great as the pressure at ab, but it works through 

 only one-tenth of the distance, thus fulfilling the law of 

 conservation of energy. You have heard of the law of the 

 indestructibility of matter. You know 

 that matter may be changed, but it 

 cannot be produced or destroyed. So 

 energy or work can be changed; the area 

 over which it operates can be multiplied. 

 But the work done cannot be multiplied. 

 Energy like matter can be changed in 

 form, as from electricity to light, but, 

 like matter, it can neither be produced 

 nor destroyed. However wonderful a 

 machine may be, the amount of work it does 

 is never greater than the amount of energy it 

 takes to make it work. The work taken out 

 cannot be greater than the work put in. 

 Water-pressure is used in the operation 

 of elevators (see Fig. 29). Water forced 

 bto the cylinder C drives back the piston 

 and produces a pull on the cable. The 

 -elevator goes up. The operator stops the car by closing 

 the valve that shuts off the water from the water-main. 

 He lowers it by opening a valve that permits the water 

 in the cylinder to run off into the sewer. City water-power 

 is also commonly used to operate pumps which pump 

 soft water into tanks at the top of houses. 



Water-Works. By water- works we mean constructions 

 ior the collection and distribution of water for towns and 



