180 CONDUCTION. 



Q. Why -is BRUTH COOLED by BLOWING it ? 



A. The breath causes a rapid change 

 of air to pass over the broth ; and (as the 

 air is not so hot as the broth) it keeps 

 absorbing heat, and thus makes the 

 broth cooler and cooler. 



Q. Would not the air absorb heat from, the 

 broth just as well WITHOUT BLOWING ? 



A. No ; air is a very bad conductor ; 

 unless, therefore, the change be rapid, 

 the air nearest the surface of the broth 

 would soon become as hot as the broth 

 itself. 



Q. But would not the hot air PABT with its 

 heat instantly to the CIRCUMJACENT air ? 



A. No ; not instantly. Air is so 

 bad a conductor, that it parts with its heat 

 very slowly : unless, therefore, the air be 

 kept in continual motion, it would cool 

 the broth very slowly indeed. 



Q. Why does WIND generally feel COOL ? 



A. Wind is only air in motion; and 

 the more quickly the air passes over our 

 body, the more rapidly it absorbs the 

 heat therefrom. 



Q. Why does AIR ABSORB heat more QUICKLY 

 !n/ briny set in MOTION ? 



