THREE METHODS OF DISTRIBUTING ,HEAT 185 









or fine kindlings, and a few small sticks on top in such a 

 way that air can circulate around the fuel. Light the paper 

 at the bottom and the fire is started. If we were to shut 

 off the upper draft in the pipe by closing the damper, or 

 if we were to close the lower door in the stove so as to 

 cut off the current of air from below, the fire would smolder 

 and go out. Air with its constant supply of oxygen is 

 necessary to keep a fire burning. We say the hot air 

 rises. But, as a matter of fact, warm air 

 is lighter than cold air and the cold air is 

 pulled downward with such force by gravity 

 that the warm air is crowded out of the 

 way. Thus smoke made up largely of hot 

 gases is pushed up the chimney. 



Three methods of distributing heat. - 

 We have all seen that heated currents of 

 air are carried up by convection. Thus heat 

 is moved about in the room by means of 

 currents of air. The air as it moves gives 

 heat to cooler bodies, and thus to a great Coi}vection currents 

 extent the rooms of our houses are warmed. j ate a r vessel of 

 But heat also moves through space where 

 there is no air. We all know that the sun keeps us warm, 

 but do we all know that its heat travels through vast 

 areas of space in which no air exists ? This space is filled 

 with ether, and through the ether heat moves by means 

 of waves. This method of heat transference is called 

 radiation. Some surfaces absorb heat much more rapidly 

 than others. Scientists know that black or dull sub- 

 stances do this much better than light or shiny substances, 

 and substances which absorb heat readily give it up 

 easily by radiation. May this be a reason for our black 



