DEVELOPMENT OF HOUSE HEATING 113 



1825. Wood was used as the fuel and the stoves were but 

 little more than open, iron fireplaces standing out in the room. 

 Between 1825 and 1835, the first stoves for burning hard coal 

 were made. Some of these were fairly successful but all have 

 been greatly improved since that time. 



129. The Invention of the Chimney. It is recorded that 

 the invention of the chimney was the result of war. At the 

 time of the Norman conquest of England in 1066 the Britons 

 heated their houses by means of fires built on the floor at 

 the center of the house. The smoke was permitted to escape 

 through a hole in the center of the roof. But the smoke so 

 bothered the Britons as they fought from the house roofs that 

 the custom arose of building a fire at one side of the room 

 and providing for the escape of the smoke through an opening 

 in the side wall. To cause the smoke to escape more readily 

 through the opening, a hood was built into the room over the 

 fire. From this crude beginning chimneys finally developed. 



CAUSES OF CONVECTION CURRENTS 



130. Some Common Observations. You have very likely 

 noticed many times that when a fire in the stove is first 

 lighted the draft is not strong for a minute or so. As soon 

 as the fire is really burning well, the draft becomes strong. 

 When we first light a bonfire, the feeble flame is blown about 

 in all directions by the breezes. When the fire gets to burning 

 fiercely, all these conditions change. Instead of being carried 

 off by the wind, the smoke and burning embers are swept swiftly 

 upward, rising in a vertical, tapering column to the height 

 of 20, 30 or perhaps 50 ft. If we notice carefully now, we 

 shah 1 see that the wind blows into the fire at the ground from 

 every direction. The rising column of air is called a CON- 

 VECTION CURRENT. We shall be able to understand this 

 better if we learn what effect the heating of air has upon its 

 volume. 



