THE STORY-BOOK OF SCIENCE 



" After acting on the piston, the steam enters the 

 same chimney that the smoke comes out of. So you 

 can see this smoke-stack sometimes throwing out 

 white puffs, sometimes black. These latter are 

 smoke coming from the furnace through the tubes 

 that go through the water; the others come from the 

 steam thrown out of the cylinders after each stroke 

 of the piston. These white puffs, in rushing vio- 

 lently from the cylinder to the smoke-stack after 

 acting on the piston, make the noise of the engine 

 as it moves." 



"I know: pouf! pouf! pouf!" exclaimed Emile. 



"The locomotive carries with it a supply of coal 

 to feed the fire, and a supply of water to renew the 

 contents of the boiler as fast as evaporation may re- 

 quire. These supplies are carried in the tender; 

 that is to say, in the vehicle that comes immediately 

 behind the locomotive. On the tender are the 

 stoker, who tends the furnace, and the engineer, who 

 controls the passage of the steam into the cylin- 

 ders." 



"The man in the picture is the engineer?" Emile 

 asked. 



"He is the engineer. He holds his hand on the 

 throttle, which allows the steam from the boiler to 

 enter the cylinders in greater or less quantity, ac- 

 cording to the speed he wishes to obtain. By one 

 movement of the throttle, the steam is cut off from 

 the cylinders and the engine stops ; by another move- 

 ment the steam is admitted and the locomotive 

 moves, slowly or rapidly at will. 



"The power of a locomotive is no doubt consid- 



