xii CONTENTS 



CHAPTER XI 



PAGE 



MAGNETISM AND ELECTRICITY 186 



Magnets. Law of Magnetic Poles. Induced Magnet- 

 ism. Nature of Magnetism. Magnetic Condition of 

 the Earth. The Dipping Needle. Electrification by 

 Friction. Two Kinds of Electricity. Conductors and 

 Insulators. Theory of Electricity. Charging a Body by 

 Induction. Storing a Charge of Electricity. Condensers. 

 - The Leyden Jar. The Electrophorus. Atmospheric 

 Electricity. Current Electricity. Kinds of Cells for 

 Producing Electricity. Effects of Electric Currents. 

 Heating Effects. Table of Resistances. Electric Light- 

 ing. Magnetic Effects of Currents. The Electromagnet. 



The Electric Bell. The Telegraph. The Telephone. 



Chemical Effects of Electricity. Electrolysis. Elec- 

 troplating. The Dynamo. Electric Motors. 



CHAPTER XII 



SOUND . . . . ; V. . . . .212 



What Causes Sound. Echoes. Musical Tones and 

 Noises. Pitch. Vibrating Strings. The Voice. The 

 Hearing. How We Hear. 



CHAPTER XIII 



LIGHT . :'.' , . 220 



Light and its Properties. Sources of Light. Lumi- 

 nous Bodies. Transparent, Translucent, and Opaque 

 Bodies. Shadows. Light as Energy. How Light is 

 Measured. The Bunsen Photometer. Reflection of 

 Light. The Reflection of Light Compared with the Reflec- 

 tion of Sound. Diffused or Scattered Light. Refraction 

 of Light. Lenses. Uses of the Lens. The Prism and 

 the Composition of White Light. Length of Light Waves. 



Absorption of Light and Color Phenomena. The Sight. 



Protection of the Eyes. Structure of the Eyeball. 

 How the Eye Does its Work. Light in the House. 

 How Glass is Made. Artificial Lighting. The Kerosene 



