XIV CONTENTS. 



Heat increases with the depth Heat in Mines and Wells Thermal 

 Springs Central Heat Volcanic Action The Heat above the Zone of Con- 

 stant Temperature entirely from the Sun The Quantity of Heat annually 

 received from the Sun Isogeothermal Lines Distribution of Heat on the 

 Earth Climate Line of Perpetual Congelation Causes affecting Climate 

 Isothermal Lines Excessive Climates The same Quantity of Heat 

 annually received and radiated by the Earth Page 273 



SECTION XXVII. 



Influence of Temperature on Vegetation Vegetation varies with the Latitude 

 and Height above the Sea Geographical Distribution of Land Plants- 

 Distribution of Marine Plants Corallines, Shell-fish, Reptiles, Insects, 

 Birds, and Quadrupeds Varieties of Mankind, yet Identity of Species 300 



SECTION XXVIII. 



Of ordinary Electricity, generally called Electricity of Tension Methods of 

 exciting Bodies Transference Electrics and Non-electrics Law of its 

 Intensity Distribution Tension Electric Heat and Light Atmospheric 

 Electricity Its Cause Electric Clouds Back Stroke Violent Effects of 

 Lightning I ts Velocity Phosphorescence Phosphorescent Action of Solar 

 Spectrum Aurora . . . 310 



SECTION XXIX. 



Voltaic Electricity The Voltaic Battery Intensity Quantity Comparison 

 of the Electricity of Tension with Electricity in Motion Luminous Effects 

 Decomposition of Water Formation of Crystals by Voltaic Electricity 

 Electrical Fish . .330 



SECTION XXX. 



Terrestrial Magnetism Magnetic Poles Magnetic Equator Lines of equal 

 Inclination The Intensity Foci of Magnetic Intensity Dynamic Equator 

 Lines of equal Intensity Form of these Lines Declination Lines of no 

 Variation Lines of equal Variation Secular Variation of the System- 

 Horary Variation Line partaking of the Horary Changes of both Hemi- 

 spheres Magnetic Storms Origin of the Mariner's Compass Natural 

 Magnets Artificial Magnets Polarity Induction Intensity Hypotheses 

 of two Magnetic Fluids Distribution of the Magnetic Fluid Electrifying 

 and Magnetizing of Light Diamagnetism 341 



SECTION XXXI. 



Discovery of Electro-MagnetismDeflection of the Magnetic Needle by a 

 Current of Electricity Direction of the Force Rotatory Motion by Elec- 

 tricityRotation of a Wire and a Magnet Rotation of a Magnet about its 

 Axis Of Mercury and Water Electro-Magnetic Cylinder or Helix Sus- 

 pension of a Needle in a Helix Electro-Magnetic Induction Temporary 

 Magnets The Galvano-Meter 355 



