288 CAUSE OF WIND. 



fire, the heat of the fire would expand 

 the air so much, that the bladder would 

 soon be entirely inflated ; (in this case, 

 the air in the bladder is expanded to 

 twice its original bulky by the heat of the 

 fire). 



Q. What EFFECT is produced upon air ly 



RAREFACTION ? 



A. It causes the air to ascend through 

 colder strata, as a cork (put at the bottom 

 of a basin of water) would ascend through 

 the water. 



Q. How do you KNOW that rarefied air 



ASCENDS ? 



A. When a boy sets fire to the cotton 

 of his balloon, the flame heats the air 

 inside the balloon ; and the air becomes 

 so light, that it ascends, and carries the 

 balloon with it. 



Q. What effect is produced upon AIR by COLD ? 



A. Air is condensed by cold, or 

 squeezed into a smaller compass; in 

 consequence of which, it becomes heavier, 

 and descends towards the ground. 



Q. How do you KNOW that air is CONDENSED 

 by COLD ? 





