FLAME. 47 



tions of air striking on the ear; so 

 light is produced by undulations of ether 

 striking on the eye. 



Q. What is ETHER? 



A. A very subtile fluid, which per- 

 vades and surrounds every thing rve see. 



Q. Mention a simple experiment to prove that 

 LIGHT is produced by rapid MOTION. 



A. When a fiddle-string is jerked 

 suddenly, its rapid vibration produces a 

 grey light ; and when a carriage wheel 

 revolves very quickly, it sends forth 

 a similar light. 



Q. Does HEAT ALWAYS produce LIGHT ? 



A. No : the heat of a stack of hay, 

 or reeking dunghill, though very great, 

 is not sufficient to produce light. 



Q. Why is a YELLOW FLA.ME brighter than a 



RED HOT COAL ? 



A. Because yellow rays always pro- 

 duce the greatest amount of light ; though 

 red rays produce the greatest amount of 

 heat. 



Q. Why is the LIGHT of afire MORE INTENSE 

 sometimes than at others ? 



