98 MECHANICAL ACTION. 



Q. What is the good of BLOWING OXYGEN 

 GAS to lighted tinder ? 



A. Oxygen gas supports combustion ; 

 and lighted tinder is quickened by the 

 breath, in the same way as a dull fire is 

 revived by a pair of bellows. 



Q. Why do HORSES sometimes STRIKE FIRE 

 with their FEET ? 



A. When iron horse-shoes strike 

 against the flint-stones of the road, very 

 small fragments (either of the shoe or 

 stones) are knocked off red-hot, and look 

 like sparks. 



Q. What makes these fragments RED-HOT? 



A. The percussion condenses the part 

 struck, and squeezes out its latent heat. 



CHAPTER VIII. 



2. FRICTION. 

 3. CONDENSATION. 



Q. What is meant by FRICTION ? 



A. The act of rubbing two things 

 together ; as the Indians rub two pieces 

 of wood together to produce fire. 



