Our Surroundings 



COLUMN* 



the 



measure height, such as the height of a mountain, 

 or the distance of an airplane above the earth. 

 When thus used it is called an altimeter. 



Atmospheric pressure changes with the weather. 

 In fact, the barometer starts to change its reading 

 of atmospheric pressure before we can see or feel 

 the change in the weather. At any fixed level a 

 falling barometer (the pressure becoming less) indi- 

 cates an approaching storm. A rising barometer 

 indicates fair weather. 



Experiments to Show Atmospheric Pres- 

 sure. To show that air exerts pressure upon sur- 

 faces because of its weight, fill a barometer tube 

 about 36 inches in length with mercury. Place a 

 finger tightly over the open end of the tube and in- 

 vert it into a dish of mercury. Then, after fastening 

 the tube to an upright standard, remove the finger, 

 taking care that no air enters the tube. Does the 

 mercury in the tube run into the dish ? If not, why ? 



To show the effect of atmospheric pressure on 

 a barometer, place a common mercurial barometer 

 where it can ( be observed frequently for a week. 

 Each day observe and record the reading of the 

 barometer. At the end of the week plot a graph 

 to show this record. 



Some Simple Experiments to Arouse 

 Thought. Blow air into an empty football, a toy 

 balloon or an automobile tire and notice that it fills 

 out evenly. What does this indicate in regard to air 

 pressure ? 



Fill with water a bent piece of tubing about 3 feet 

 long and close both ends of the tube. Place one end 

 in a pail of water on a table, and the other end in 

 a pail on the floor. Then open both ends of the 

 tube. Does the water run out of the upper pail? 



If S0 Whv? A bent tube USCd in this Wa y t0 



liquid from one level to another is called a s 



