Put your hand over a lamp chimney under which the lamp is lighted. You will soon discover that the heat is rising. Four things in connection with this are of great importance:
1. Air has weight. 2. When heated, it rises. 3. Air expands when heated. 4. Warm air will gather and hold more moisture than cold air.
EXPERIMENT NO. 6
Cut a piece of stiff cardboard in a spiral shape. Thread a piece of thread through a pinhole in the center point of the spiral and fasten this to a support so that it swings freely in the air. (See Fig. [8].) Under this put a little alcohol lamp, or put it over a gas jet or radiator.
WHAT HAPPENS
The cardboard will spin around rapidly. Ask yourself what causes this. It is the force of the hot air rising which caused the spiral cardboard to turn in such an attractive manner.
EXPERIMENT NO. 7
Fig. 9
When you are in a warm room, find out which air is the hottest, that in the upper or that in the lower part of the room. This answer you can get by placing the thermometer low down in the room and then putting it up near the ceiling. This is another conclusive proof that hot air rises.