54 GENERAL SCIENCE 



If we now increase the pressure or weight on the vacuum cnamber, it 

 pulls the spring down with it; if we decrease the pressure, the spring opens 

 it up proportionately. 



It is now easy to see that this spring moves up or down as the air pressure 

 decreases or increases. If we secure an arm to it we will magnify its move- 

 ment at the end of the arm. 



H. Bar, or arm, compensated for .temperature, which at its end magnifies 

 movement of the spring F. 



L. L. Two supports or pillars fitted to plate A. 



FIG. 47. 



Description. The dials are divided into inches of mercury 

 pressure. If the barometer is standing at 29 it means that at that 

 point of observation mercury would be supported at a height of 29 

 inches in a tube, as explained in Torricelli's experiment. 



The Pressure of the Air Does not Decrease Evenly. By the 

 table it will be seen that the drop in the barometer between 31 and 

 30 inches represents a rise of 890 feet. Between 17 and 18 inches 

 the rise would be 1580 feet. 



QUESTIONS 



1. During a stormy day the barometer dropped 1.5 inches. 

 How far would a water barometer have dropped? What was the 

 pressure of the atmosphere in pounds per square inch? 



2. How far would a perfect suction pump lift water in your town? 



3. Why does the barometer work as well inside as outside of a 

 building? 



4. Why is it better to keep a barometer in the same room and 

 inside of a building, especially if it is not compensated? 



5. How could one remove the water from a boat on the beach 

 with a rubber hose? 



Why is it impossible to use the same method to get the bilge 

 water out of a boat floating on the water? 



