[Illustration:
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.
Another experiment that is quite familiar to all of us is that of
opening the windows of a heated room a few inches top and bottom, and
holding a lighted match or smoke paper at the bottom, when you will find
that it blows the flame or smoke inward. Then put it near the top of the
window and it will be drawn out. The same answer is true; the cold air
is rushing in from below to take the place of the hot air rising and
going out at the top. (See Fig. 9.)
[Illustration:
Fig. 10
]