NON-LIVING THINGS 2O/ 



paper 1 over the opening under which the lighted candle 

 was placed. The smoke from the punk indicates the true 

 direction of the air current. Now hold the punk near the 

 other opening. In which direction is the air moving here? 

 Which is lighter, air that is expanded by heat or cold air? 

 Explain the direction of the currents as shown by the move- 

 ments of the smoke. Take the temperature of the school- 

 room at the floor and at the ceiling. Where is the warmer 

 air? Why? 



Close the openings at the top of the box and open two 

 at the end, one near the bottom, the other near the top. 

 Test with the burning punk as before. Which shows an 

 inflowing current, the upper or the lower opening? Is air 

 flowing out of the other opening? Explain. Make clear 

 the cause of the currents thus set up. Does the cooler, 

 heavier air flow in to take the place of the warm air that is 

 rising, or does the cooler air, owing to its greater weight, 

 cause the warmed air to rise? 



On a quiet day, when there is a brisk fire in the school- 

 room, close all openings except one window. This should 

 be open at both top and bottom for six inches or a foot. 

 Test the air at the bottom to find the direction of the cur- 

 rent by suspending a light sheet of paper from the lower 

 edge of the window sash. Test in the same way the cur- 

 rent through the upper opening. If conditions are favor- 

 able the results will speak for themselves very definitely. 

 Now open the window from the bottom only by raising 

 both sashes as high as possible. Test the upper and lower 



1 Touch paper is easily made by soaking blotting paper in a sat- 

 urated solution of saltpeter. When dry the paper burns slowly 

 and with much smoke, making a good substitute for Chinese punk 

 sticks. 



