AIR. VIII. 



35. A brief summary of the facts stated under the 

 same topic in the work for fifth, sixth, and 



seventh grades. 

 35. Humidity in the air. 



a. Absolute. 



b. Relative. 



Experiment 28. The dew-point. 

 Experiment 29. The wet-bulb thermom- 

 eter. 



37. Rain. 



a. Cause. 



Experiment 30. Cooling by expansion. 



b. Measurement valuable. 



Experiment 31. The rain-gauge. 



38. Snow and hail. 



a. Cause. 



b. The shape of ice crystals. 



Experiment 32. Copying microphoto- 

 graphs of snow flakes. 



39. Ice. 



a. Icebergs and glaciers. 



b. Why ice floats. 



Experiment 33. The space occupied by 

 melting ice. 



40. Painting. 



a. For adornment. 



b. For preservation from the weather. 



Experiment 34. Preservation of wood 

 and metal. 



41. Atmospheric electricity. 



a. Lightning. 



