CLIMATES OF A ROOM.
The air in a room may be said to resemble two climates: as it is lighter than the external air, a current of colder or heavier air is continually pouring in from the crevices of the windows and doors; and the light air must find some vent, to make way for the heavy air. If the door be set a-jar, and a candle held near the upper part of it, the flame will be blown outwards, showing that there is a current of air flowing out from the upper part of the room; and, if the candle be placed on the floor, close by the door, the flame will bend inwards, showing that there is also a current of air setting into the lower part of the room. The upper current is the warm, light air, which is driven out to make way for the stream of cold, dense air, which enters below.