216 



WEATHER AND CLIMATE 



FIGURE 87 



waters and from the parched places of the earth. By its 

 movements, it keeps the very fires of man's factories and 

 engines burning, sweeps the smoke and foul air away from 

 his cities, and bears his commerce across the sea. 



Wind. Experiment 75. On a day when the temperature in 

 the room is considerably higher than that outside, open a window 



at the top and bottom and hold a 

 strip of tissue paper in front of the 

 opening. Is there an air current, 

 and if so, in what direction does it 

 move at the top and at the bottom 

 of the window ? What causes 

 "drafts "in a room? 



Experiment 76. Procure two 



similar dishes about 15 cm. high and 5 or 6 cm. in diameter with 

 short tubes of about 1 cm. in diameter opening out from near the 

 top and bottom. Connect the bottom tubes of the two dishes 

 with a tightly fitting rubber tube. Do the same with the top 

 tubes. Place a Hoffman's screw upon each of the rubber tubes 

 and screw it tight so that no liquid can flow through either tube. 

 (If part of each rubber tube is replaced by a glass tube, 

 the action hi the experiment can be seen to better 

 advantage.) Fill one of the dishes with colored water 

 and the other with kerosene or some light oil. 



Release the Hoffman's screw upon the top tube and 

 then the one at the bottom. Notice carefully what 

 happens as the lower tube is allowed to open. The 

 dishes are not now filled with oil and water respec- 

 tively. In the transfer of the liquids, through which 

 tube did each pass ? FIGURE 88 



Experiment 77. Fill a convection apparatus with 

 water, putting in a little sawdust and mixing it well with the 

 water. Heat one side of the tube and observe the convection 

 currents set up. 



In Experiment 76 the interflow from one dish to the other 

 is due to the fact that the water is heavier than the oil and 



