The mechanism of the dynamo, p. 173--The origin of the dynamo, p. 176--The work of Ampère, Henry, and Faraday, p. 177--Perfecting the dynamo, p. 178--A mysterious mechanism, p. 180--Curious relation between magnetism and electricity as exemplified in the dynamo, p. 182. CHAPTER X NIAGARA IN HARNESS The volume of water at the falls, p. 184--The point at which the falls are "harnessed," p. 185--Within the power-house, p. 186--Penstocks and turbines, p. 188--A miraculous transformation of energy, p. 189--Subterranean tail-races, p. 191--The effect on the falls, p. 192--The transmission of power, p. 194--"Step-up" and "step-down" transformers, p. 198. CHAPTER XI THE BANISHMENT OF NIGHT Primitive torch and open lamp, p. 202--Tallow candle and perfected lamp, p. 205--Gas lighting, p. 207--The incandescent gas mantle, p. 208--Early gas mantles, p. 209--How the incandescent gas mantle is made, p. 211--The introduction of acetylene gas, p. 212--Chemistry of acetylene gas, p. 214--Practical gas-making, p. 215--The triumph of electricity, p. 218--Davy and the first electric light, p. 220--Helpful discoveries in electricity, p. 222--The Jablochkoff candle, p. 223--Defects of the Jablochkoff candle, p. 225--The improved arc light, p. 226--Edison and the incandescent lamp, p. 228--Difficulties encountered in finding the proper material for a practical filament, p. 230--"Parchmentized thread" filament, p. 233--The tungsten lamp, p. 234--The mercury-vapor light of Peter Cooper Hewitt, p. 236--Advantages and peculiarities of this light, p. 240. CHAPTER XII THE MINERAL DEPTHS Early mining methods, p. 242--Prospecting and locating mines, p. 243--"Booming," p. 246--Conditions to be considered in mining, p. 248--Dangerous gases in mines, p. 249--Artificial lights and lighting, p. 251--Ventilation and drainage, p. 252--Electric machinery in mining, p. 253--Electric drills, p. 254--Traction in mining, p. 256--Various types of electric motors, p. 257--"Telphers," p. 261--Electric mining pumps, p. 263--Some remarkable demonstrations of durability of electric pumps, p. 265--Electricity in coal mining, p. 266--Electric lighting in mines, p. 269. CHAPTER XIII THE AGE OF STEEL Rapid growth of the iron industry in recent years, p. 271--The Lake Superior mines, p. 272--Methods of mining, p. 273--"Open-pit" mining, p. 274--Mining with the steam shovel, p. 276--From mine to furnace, p. 278--Methods of transportation, p. 279--Vessels of special construction, p. 281--The conversion of iron ore into iron and steel, p. 283--Blast furnaces, p. 284--Poisonous gases and their effect upon the workmen, p. 286--From pig iron to steel, p. 287--Modern methods of producing pig iron, p. 288--The Bessemer converter, p. 289--Sir Henry Bessemer, p. 291--The "Bessemer-Mushet" process, p. 293--Open-hearth method, p. 294--Alloy steels, p. 295. CHAPTER XIV