WATER-POWER AND STEAM-POWER 77 



Water-Power and Steam-Power Compared. They are 

 alike in that they both use water. But let us note an 

 apparent difference as to the force behind. You have noted 

 that the force behind water-power is the force of gravity. 

 There is no water-power unless the water falls. Thus 

 it is gravity, acting on water, that is the real force that 

 turns the turbines, that spins the generators, that gener- 

 ates the electricity, that lights the electric lamp by whose 

 light, even now, you may be reading these words. 



In steam-power, however, it is heat that is the force 

 behind. It is heat that expands the water into steam, 

 and then expresses itself in pressure if this steam is con- 

 fined. This heat, in turn, is generated by the burning of 

 fuel. Whether the fuel be coal or wood, its source is 

 plants, for coal is a formation of ancient plants (see page 

 49). Now since we can release it by burning, there must 

 be energy in the wood and coal. Where did they get it? 

 They got it from the sunlight which once shone on the 

 leaves of the plants of which they were a part. So, if it 

 be that the wire from your electric lamp runs to a steam- 

 operated electric plant, it is the force of the sunlight of 

 ancient days which is now expressing itself in the light 

 you read by. Think, then, how these two ancient forces, 

 gravity and sunlight, serve us to-day. Whether it be the 

 light by which we read, the trains by which we travel, the 

 wires over which we send our messages, the automobiles 

 in which we ride, or any one of a thousand other of our 

 modern conveniences, we can trace all back to the source 

 of their power, and find it in one or the other of these great 

 servants of mankind, the pull of this old earth we live on 

 and the sunlight which shines upon it. Yet we should 

 remember that before the "pull of earth" can act on water, 



