Through machines 

 man has developed elec- 

 tricity, thus furthering 

 his control of his en- 

 vironment. 



CONTENTS 



CHAPTER XVI. Two^ RELATED FORCES 

 THAT MAN HAS HARNESSED MAGNETISAT AND 

 ELECTRICITY 



Magnetism Magnetic Field of Force Mar- 

 iner's Compass Theory of Magnetism 

 Electricity by Friction Current Electricity : 

 Electric Lighting, Electroplating The Elec- 

 tromagnet : Electric Bell, Telegraph, Wireless 

 Telegraph, Telephone The Dynamo The 

 Electric Motor Theory of Electricity . 475 



Magnets. Dipping needle. Positive and negative 

 poles. Conductors and non-conductors. Cells. 

 Flatirons and toasters. Welding. Electrotyping. 

 Magnetic crane. 



This chapter is de- 

 voted to the mysteries of 

 the sub-surface earth, 

 following naturally 

 after the treatment of 

 various aspects of sci- 

 ence on the earth. 



This final chapter 

 contains a general dis- 

 cussion of .the relation 

 of life to physical en- 

 vironment. 



The projects develop 

 practical knowledge by 

 personal investigation. 



CHAPTER 

 CRUST 



XVII. WITHIN THE EARTH'S 



Volcanoes Earthquakes Geysers Mining 

 The Story of Coal and Oil . . .502 



Craters. Lava and volcanic dust. Vesuvius and 

 Mt. Pelee. The Yellowstone. Mining districts of 

 the United States. 



CHAPTER XVIII. LIFE 

 PHYSICAL CONDITIONS 



AS RELATED TO 



Ancient Life History Distribution of Life 

 Effect of Glacial Period on Plants and Animals 

 Adaptability of Life Plant and Animal 

 Life in the Sea Life on the Land Distri- 

 bution of Animals Life on Islands Man 

 Affected by Physical Features . . 522 



Fossils. Petrified trees. Barriers to distribution. 

 Inland and seashore life. Strange plants and 

 animals. Effect of mountains on history. Ad- 

 vantages of harbors. 



APPENDIX 555 



PROJECTS 563 



INDEX . 1 



