BAROMETER. 325 



A. If (in frosty weather) it begins to 

 snow, the barometer generally rises to 

 32, where it remains as long as the 

 snow continues to fall; if, after this, 

 the weather clear up, you may expect 

 very severe cold. 



Q. How can you know if the MERCURY of the 

 barometer be RISING ? 



A. If it be convex (i. e. higher in the 

 middle than at the sidesj it is in a rising 

 state. 



Q. How can you tell if the MERCURY of the 

 barometer be about to FALL ? 



A. If it be concave (i. e. hollow in the 

 middle) it is in a falling state. 



Q. Why is the mercury CONVEX when it is 



RISING ? 



A. The sides of the mercury rub 

 against the glass tube, and are delayed 

 by it, so that the middle part rises faster 

 than the sides. 



Q. Why is the mercury CONCAVE when it is 



FALLING? 



A. The sides of the mercury rub 

 against the glass tube, and are delayed by 

 it, so that the middle part sinks faster 

 than the sides. F a 



