CHAPTER XXIII.
BAROMETER.
Q. What is a barometer?
A. A weather-glass, or instrument to show the changes of the weather, by marking the variations in the weight of air.
Q. What is a thermometer?
A. An instrument to show how hot or cold anything is.
Q. What is the difference between a thermometer and a barometer?
A. In a thermometer the mercury is sealed up from the air:
In a barometer the mercury is left exposed (or open) to the air.
Q. If the mercury of the thermometer be sealed up from the air, how can the air affect it?