BAKOMETEB. 317 



CHAPTER XXIII. 

 BAROMETER. 



Q. What is a BAROMETEK? 



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 THER- 

 MOMETER 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 /row the air, how can the air AFFECT it ? 



A. The heat of the air passing through 

 the glass tube into the mercury, causes it 

 to expand more or less, and rise in the 

 tube accordingly. 



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