TABLE OF CONTENTS ix 



PAGE 



57. Barometers: Mercurial; Aneroid; Barograph . . 119 



58. Determination of Height by a Barometer . . .122 



59. Adiabatic Heating and Cooling of Air ... 123 



60. Effect of Temperature on the Opacity of the Air to 



hold Moisture ; Dew Point 124 



61. Moisture in the Atmosphere ; Evaporation . . 125 



62. Humidity; Clouds; Fog; Dew; Hygrometer . .126 



63. Effect of Atmospheric Conditions on Light ; Coronas ; 



'Halos ; Mirages; Aurora Borealis . . .127 



64. The Warming of the Atmosphere ; Radiation ; Inso- 



lation 130 



65. Cause of the Variation in Atmospheric Temperatures ; 



Directness of Rays ; Height above Sea ; Nearness 



to Sea 131 



66. Graphic Method of showing the Temperature of a 



Region; Isotherms; Isobars . . . .134 



67. Weather Maps 138 



68. Land and Water Temperatures ; Ocean Winds . .139 



69. Distribution of Air Pressure over the Earth ; Baro- 



metric Gradients . . . . .139 



70. Wind ; Barometric Pressure 1 42 



7 1 . Velocity and Effect of Wind Action ; Anemometer ; 



Windmills; Sailing Vessels . . . . 144 



72. The Effect of the Earth's Rotation on Winds; Fer- 



rers Law . . . . . . . .146 



73. Planetary Wind Belts; Heat Equator: Terrestrial 



Winds 148 



74. Wind Belts of the Earth ; Doldrums ; Trade-winds ; 



Horse Latitudes . . . . .1 49 



75. Land and Water Winds ; Effect on Climate . . 152 



76. Monsoons ; Effect on Trade . . . . .153 



77. Rainfall and its Measurement ; Rain-gauge ; Snow ; 



Sleet; Hail 154 



78. Rainfall of the United States ; Irrigation . . .157 



79. Electricity ; Positive and Negative ; Conductors and 



Nonconductors . . . . . . .160 



80. Thunder-storms ;. Electrical Charges and Discharges ; 



Lightning . . . . . . . .163 



8 1 . Electrical Communication ; Batteries ; Telephone ; 



Telegraph; Wireless 165 



82. Tornadoes and Waterspouts . . . ..167 



83. Cyclones; Anticyclones 168 



