472 TRANSFERRING AND TRANSFORMING ENERGY 



steam under great pressure to a wheel somewhat similar 

 in construction to a water turbine. Thus steam is made to 

 give a rotary motion, instead of the back and forth motion 

 of the ordinary steam engine, which must be converted into 

 rotary motion by the connecting rod and crank. These 

 steam turbines, as they are called, have been used to great 



advantage in ocean ves- 

 sels where there is little 

 space available for ma- 

 chinery and where great 

 power and high speed 

 are desired. 



In the gas engine the 

 energy of gas exploding 

 in a cylinder behind a 

 piston takes the place of 

 expanding steam in driv- 

 FIGUBE 147 ing the piston. Usually 



two or more cylinders 



are. used, and the explosions are so timed that a very steady 

 motion is given to the shaft. These engines were first 

 made about fifty years ago but have been greatly improved 

 recently, and are now used very extensively for automobiles, 

 motorboats, and airplanes. 



The electric dynamo and the electric motor, which will 

 be discussed later, are other energy transformers which man 

 has developed and now constantly uses. 



Power Available to Man. When combustion is used as 

 a source of energy, man is drawing upon his bank account 

 with nature, and is using up the stored energy of the earth. 

 But in utilizing the energy of blowing wind and running 



