220 THE STORY-BOOK OF SCIENCE 



bottle, but also the thickest, most solid pots of iron, 

 bronze, or any other very resistant material. Is it 

 necessary to say that under those conditions the ex- 

 plosion is terrific! The fragments of the pot are 

 thrown with a violence comparable to that of a can- 

 non-ball or a bursting bomb. Everything standing 

 in the way is broken or knocked down. Powder 

 does not produce more terrific results. What I 

 have just shown you with the glass vial is also not 

 without some danger. You can be blinded with this 

 dangerous experiment, which it is well to see once 

 under proper precautions, but which it would be 

 imprudent for you to repeat. I forbid you all, un- 

 derstand, to heat water in a closed vial ; it is a game 

 that might cost you your eyesight. If you should 

 disobey me on this point, good-by to stories; I 

 would not keep you with me any longer. ' ' 



" Don't be afraid, Uncle, " Jules hastened to in- 

 terpose; "we will be careful not to repeat the exper- 

 iment ; it is too dangerous. ' ' 



"Now you know what makes the locomotive and 

 a great many other machines move. In a strong 

 boiler, tightly closed, steam is formed by the action 

 of a hot furnace. This steam, of an enormous 

 power, makes every effort to escape. It presses 

 particularly on a piece placed for that purpose, 

 which it chases before it. From that a movement 

 results that sets everything going, as you will see 

 in the case of the locomotive. To conclude, let us 

 remember that in every steam engine the essential 

 thing, the generator of the force, is a boiler, a 

 closed pot that boils." 



