CONTENTS 

 PART I. THE AIR 



PAGE 



CHAPTER I. SOME CHARACTERISTICS OF THE AIR .... 1 



Air as material. Working under water. The weight of air. Air 

 pressure. Measurement of air pressure. Graduation of the barom- 

 eter. Altitude and air pressure. Effect of temperature. Thermom- 

 eters. Some effects of expansion. Convection currents. Hot-air 

 furnaces. Chimneys. Importance of air temperature. 



CHAPTER II. TEMPERATURE CHANGES AND THE SEASONS 16 

 Seasonal changgs of temperature. Relation of the seasons to the 

 sun. Effects of changes in sun's altitude. Length of day and 

 night. How the air is warmed. 



CHAPTER III. THE WATER OF THE AIR 21 



Evaporation. Amount of water in the atmosphere. Absolute hu- 

 midity and relative humidity. Some examples. Determination of 

 relative humidity. Variations in relative humidity. Humidity in 

 houses. Total amount of water in the air. 



CHAPTER IV. THE WEATHER 28 



General statement. Air pressure and winds. Pressures as shown by 

 weather maps. Procession of high and low pressures. Winds about 

 a "low" cyclones. Temperature in a cyclone. Humidity in a 

 cyclone. Passage of a cyclone. Weather in anticyclones. Hot and 

 cold waves. Hurricanes. Thunderstorms. Tornadoes. General 

 circulation of air on the earth. Rainfall in the United States. 

 The United States Weather Bureau. 



CHAPTER V. STRUCTURE OF AIR: MOLECULAR THEORY 49 



Compressibility of air. Expansion of gases. Diffusion of gases. 

 Some questions regarding gases. A theory about the air. Molecular 

 theory applied to air. Gas pressures. Heat and molecular move- 

 ment. Gas mixtures. Liquids and solids. 



CHAPTER VI. COMPOSITION OF AIR : ATOMIC THEORY . . 55 

 The air not a simple substance. The flame and the air. A burning 

 candle. Products of the flame. Water produced by a flame. The 



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