318 BAROMETER. 



Q. Why is the TUBE of a BAROMETER left 

 OPEN ? 



A. That the air may press upon it 

 freely; and as this pressure is more or 

 less, the mercury rises or falls in the tube, 



Q. How can weather be affected by the WEIGHT 

 of the air? 



A. When air is warm or moist, it is 

 lighter than usual : 



When it is cold or dry, it is heavier : 

 and as a barometer marks whether the 

 air be light or heavy, it indicates these 

 changes. 



Q. How can you tell (by looking at a 

 BAROMETER) what KIND of WEATHER it will bep 



A. Because the mercury in the tube 

 rises and falls, as the air becomes lighter 

 or heavier : and we can generally tell by 

 the weight of the air, what kind of weather 

 to expect. 



Q. Does the WEIGHT of the air VARY MUCH ? 



A. Yes ; the atmosphere in England 

 varies as much as one-tenth part more or 

 less. 



Q. Wliat is the chief USE of a BAROMETER ? 



A. To warn sailors how to regulate 

 their ships, before squalls come on. 



