NON-LIVING THINGS 



Other manifestations and uses of air pressure are seen in 

 the use of the siphon and the common lifting pump. 



The measure of air pressure may be taken up with pupils 

 of the sixth grade and above. Introductory to the work 

 of making a barometer the follo'^^tigf will be helpful : Bend 

 a piece of glass tubing into the form of the letter U. Fill 

 the bend of the tube with mercury, and have the class note 

 that when the tube is perpendicular the mercury stands at 

 the same height in both sides. Call attention to the fact 

 that the air presses with equal weight on the mercury in 

 both tubes. Ask the class what would be the effect of blow- 

 ing into one of the tubes, thus increasing the pressure on 

 that side. This they will readily see. What is the effect 

 of sucking some of the air out of one of the tubes ? Why ? 

 Be sure that the class sees that difference in the force of 

 air pressure makes the mercury stand higher in the tube 

 in which the air pressure has been reduced by drawing out 

 some of the air. 



The making of the barometer should follow. For this 

 the following will be needed : A piece of glass tubing about 



thirty-six inches long and one-fourth of an 

 Barometer 



inch in diameter inside. This tube should 



be closed at one end. A piece of tube, the same diameter, 

 twelve inches long, and open at both ends. Two pieces of 

 strong rubber tubing, about six inches long, and large 

 enough to fit snugly over the ends of the glass tubes. 

 Enough mercury to a little more than fill the longer tube. 

 A small funnel having a stem equal in diameter to that of 

 the glass tube. 



Connect the open end of the long tube to the shorter tube 

 by means of the rubber hose. This should be tied tightly 



