56 THE EEASON WHY. 



1 The fear of the Lord is the beginning of knowledge : but fools despise wisdom 

 and instruction." PKOVEKBS I. 



the body, and passing over it leave some portion of their heat be- 

 hind, which is again followed by additional heat from every fresJi 

 blast of wind. 



CHAPTER IX. 



181. What is Eadiation ? 



The radiation of heat is a motion of the particles, in a series of 

 rays, diverging in every direction from a heated body. 



182. What is this phenomena of Radiation understood to 

 arise from ? 



From a strongly repulsive power, possessed by particles of heat, 

 by which they are excited to recede from each other with great 

 velocity. 



183. What is the greatest source of Radiation ? 



The sun, which sends forth rays of loth light and heat in all 

 directions. 



184. When does a body radiate heat ? 



When it is surrounded by a medium which is a bad conductor 



185. When we stand before a fire, does the heat reach us 

 by conduction or by radiation ? 



By radiation. 



186. What becomes of the heat that is radiated from one 

 body to another ? 



It is either absorbed, by those bodies, or transmitted through them 

 and passed to other bodies by conduction, or diffused by convection, 

 or returned by refiection. 



187. How do we know that heat is diffused by radiation ? 



If we set a metal plate (or any other body, though metal is 

 host for the experiment) before the fire, rays of heat will fall upon 

 it. If we turn the plate at a slight angle, and place another 



