WIND. 287 



arisen from the ignited gas of church- 

 yards lurking about the tombs, to which 

 fear has added its own creations. 



CHAPTER XXII. 



WIND. 



Q. What is WIND ? 



A. Wind is air in motion. 



Q. What PUTS the air in motion, so as to 

 produce WIND ? 



A. The principal causes are the 

 variations of heat and cold, produced by 

 the succession of day and night, and the 

 four seasons. 



Q. What effect has HEAT upon the air ? 



A. Heat rarefies the air, and causes 

 it to expand. 



Q. How do you KNOW that heat causes the 

 air to EXPAND ? 



A. If a bladder half full of air (tied 

 tight round the neck), were laid before a 



