How Air Comes In and Goes Out of a Room
This is an experiment which can best be performed on a winter’s evening when your dining-room is nice and warm because the fire has been alight for some hours.
Just open the door an inch or more and hold a lighted candle near the opening. First, we want you to place it on the floor level. Notice the flame. It will be blown away from the door, towards the fireplace. Second, place it near the top of the door. The flame is now blown towards the door and away from the fireplace. Third, hold it halfway up the door. The flame is more or less in a vertical or normal position. The question is, :”What can we deduce from these positions of the flame?” Just this : The fire warms the room and the air is made to expand.
How air is lighter than cold air, so it rises. In rising, it makes the middle or third flame rise with it. As the hot air goes up, cold air rushes into the room at a low level to take its place. The inward rush causes the first flame to be blown towards the fireplace. As hot air is constantly being, some of it must be pushed out of the room. Therefore the second flame pointed towards the door.