104 EFFECTS OF HEAT. 



Q. Why do unslit CHESTNUTS CBACK with 

 a loud noise, when BOASTED ? 



A. Chestnuts contain a great deal of 

 air, which is expanded by the heat of the 

 fire ; and, as the thick rind prevents the 

 air from escaping, it violently bursts 

 through, slitting the rind, and making a 

 great noise. 



Q. What occasions the loud CRACK or 

 report which we hear ? 



A. 1st The sudden bursting of the 

 rind makes a report, in the same way as 

 a piece of wood or glass would do, if 

 snapped in two : and 



2ndly The escape of hot air from 

 the chestnut makes a report also, in the 

 same way as gunpowder, when it escapes 

 from a gun. 



Q, Why does the sudden BURSTING of the 

 rind, or SNAPPING of a piece of wood, make a 

 REPORT ? 



A. As the attraction of the parts is 

 suddenly overcome, a violent jerk is 

 given to the air; this jerk produces 

 rapid undulations in the air, which 

 ('striking upon the ear) give the brain 

 the sensation of sound. 



