ATMOSPHERIC PRESSURE AND THE BAROMETER 113 



4. 1803 : 59-63. The Barometer. 



a. 1102:82-83. The Barometer. 



6. 1302 : 275-276. The Barometer. 



c. 1303 : 24-27. Pressure of the Atmosphere. 



d. 1309 : 203-204. The Barometer. 



e. 1310 : 374-375. The Barometer and Altitude. 

 /. 1801 : 122-126. The Barometer. 



g. 1802 : 120-124. The Barometer. 



h. 1804 : 157-163. How Atmospheric Pressure is Measured. 



i. 1805 : 139-143. The Barometer. 



j. 1807 : 33-36. Measurement of Atmospheric Pressure. 



k. 1808 : 145-148. Measurement of Atmospheric Pressure. 



Experiment 42. Atmospheric Pressure. 



Apparatus: Glass tumbler, card to cover it, glass tube \" 

 diameter, 40" long and closed at one end, small funnel, evap- 

 orating dish, ring stand, meter stick, iron pan, piece of cloth. 



Materials: Mercury. 



a. Fill the tumbler full of water, place the card over it, and, 

 gently pressing on the card, invert the glass and card. Then 

 remove the hand from the card, which will stay in place. 

 What holds it there ? By placing the inverted glass on a 

 smooth table, the card may be removed, leaving the glass full 

 of water, but inverted. How can such a glass of water be 

 removed from the table without spilling any of the water? 



b. Place the closed end of the glass tube upon the cloth, 

 used as a pad in the pan, and fill with mercury, using the 

 funnel. Half fill the evaporating dish with mercury, and, 

 holding one finger firmly over the open end of the tube, 

 invert it in the evaporating dish. Clamp the tube in 

 the ring stand. How high does the mercury in the tube 

 stand above the surface of mercury in the evaporating dish ? 

 Why is it not 30"? Do you think that there is a vacuum at 

 the top of the tube? 



