MAPS AND ILLUSTRATIONS 



PAGE 



The Climax of Scientific Achievement Conquest of the Air Frontispiece 

 Mt Wilson Solar Observatory, the 150-foot Tower Telescope . . 1 



Surface Explosions on the Sun . . 3 



Sun Spots 4 



Part of the Milky Way . . . . . . . . , . 5 



A Star Cluster . .-._'".. ... 6 



A Continuous Picture of the Northern Heavens . ... 7 



Medieval Idea of the Universe 9 



A Large Meteorite , , 12 



Mars . . . . . , - 13 



Three Views of Saturn 14 



Surface of the Moon . 14 



Phases of the Moon . 15 



Total Eclipse of the Sun ..16 



Halley's Comet 17 



The W T orld According to Hecataeus (500 B.C.) . . . . . 20 



Partial Eclipse of the Moon 22 



A Hut in the Tropics 30 



A Laplander's Hut . . 31 



Map showing Standard Time Belts 34 



Map showing International Date Line 36 



Region around the North Magnetic Pole 38 



Airplanes . . .'.... !.'-,... v * . . . 45 



Three Forces in Play . >,. . ,48 



^Rusting of Iron ' . \ . . . . 54 



Rock Salt . . . . ' . ,. . . i . . . 55 



Kettle Used in Manufacture of Soap . . ..-.,. . . 56 



A Pile Driver in Action . . . . * . . .61 



Molten Steel Flowing from a Blast Furnace . ,_, . ... 69 



Tinder Box and Flint and Steel v . . / . 



Before Installing an Underfeed Furnace ....*. 76 



After Installing an Underfeed Furnace . . . , . ..77 

 Fire out of Control . . : ... ,". -,. ... 78 

 Revolving Doors . . .';... . . . .91 



xi 



