102 MECHANICAL ACTION. 



together} their particles are compressed, 

 and this latent heat rolls out and melts 

 the ice. 



Q. Are not FORESTS sometimes SET on FIRE 

 by friction ?* 



A. Yes - 9 when two branches or 

 trunks of trees (blown about by the 

 wind) rub violently against each other, 

 their latent heat is developed, and sets 

 fire to the forest. 



Q. What is meant by COMPRESSION ? 



A. The act of bringing parts nearer 

 together ; as a sponge is compressed by 

 being squeezed in the hand. 



Q, Cannot HEAT be evolved from common air 

 merely by COMPRESSION ? 



A. Yes ; if a piece of German tinder 

 be placed at the bottom of a glass tube, 

 and the air in the tube compressed by a 

 piston,* the tinder will catch fire. 



Q. Why will the tinder catch Jire ? 



A. Because the air is compressed ; 

 and its latent heat being squeezed out, 



* In a common syringe or squirt, the handle part which 

 contains the sucker (and is forced up and down), is called 

 " The Piston." 



