196 RADIATION. 



Q- WHEN is heat RADIATED from one body 

 to another ? 



A. When the two bodies are sepa- 

 rated by a non-conducting medium : thus 

 the sun radiates heat towards the earth, 

 because the air comes between (which is 

 a very bad conductor). 



Q. On WHAT does RADIATION DEPEND ? 



A. On the roughness of the radiating 

 surface : thus if metal be scratched, its 

 radiating power is in creased, because the 

 heat has more points to escape from. 



Q. Does a FIRE RADIATE heat ? 



A. Yes; and because burning fuel 

 emits rays of heat, therefore we feel warm 

 when we stand before a fire. 



Q. Why does our FACE FEEL uncomfortably 

 HOT, when we approach a FIRE ? 



A. Because the fire radiates heat 

 upon the face ; which (not being covered) 

 feels the effect immediately. 



Q. Why does the fire catch the FACE more 

 than the REST of the body ? 



A. The rest of the body is covered 

 with clothing, which (being a bad con- 

 ductor of heat) prevents the same sudden 



