Vol. II., p. 111 _seq._, for an account of William Gilbert's study of magnetism; pp. 213, 215 describing first electrical machine; and chapter XIV., "The Progress of Electricity from Gilbert and Von Guericke to Franklin," p. 259 _seq._ Vol. III., chapter VII., "The Modern Development of Electricity and Magnetism," p. 229 _seq._ Vol. V., p. 92 _seq._, the section on Prof. J. J. Thompson and the nature of electricity. Other chapters that may be advantageously reviewed in connection with the present one are the following: Vol. III., chapter VI., "Modern Theories of Heat and Light," p. 206 _seq._; chapter VIII., "The Conservation of Energy," p. 253 _seq._; and chapter IX., "The Ether and Ponderable Matter," p. 283 _seq._ CHAPTER IX MAN'S NEWEST CO-LABORER: THE DYNAMO The references just given for chapter VIII. apply equally here. The experiments of Oersted and Faraday are detailed in vol. III., p. 236 _seq._ CHAPTER X NIAGARA IN HARNESS Same references as for chapters VIII. and IX. CHAPTER XI THE BANISHMENT OF NIGHT (p. 221). Davy and the electric light. The quotation here given is reproduced from vol. III., pp. 234, 235. The very great importance and general interest of the subject seem to justify the repetition, descriptive of this first electric light. Davy's original paper was given at the Royal Institution in 1810. (p. 237). "Peter Cooper Hewitt--Inventor," by Ray Stannard Baker, in _McClure's Magazine_, June, 1903, p. 172. In connection with the problem of color of the light emitted by Mr. Hewitt's mercury-vapor tube, the chapter on "Newton and the Composition of Light" (vol. II., p. 225 _seq._) may be consulted. Also "Modern Theories of Heat and Light," vol. III., p. 206 _seq._ CHAPTER XII THE MINERAL DEPTHS The chapter on "The Origin and Development of Modern Geology," vol. III., p. 116 _seq._, may be read in connection with the allied subjects here treated. In preparing the section on the use of electricity in mining, the article by Thomas Commerford Martin, entitled _Electricity in Mining_, in the United States _Census Report_ of 1905, has been freely drawn upon. The quotations on pp. 262, 266, 268, and 270 are from that source. CHAPTER XIII THE AGE OF STEEL See note under chapter XII. CHAPTER XIV SOME RECENT TRIUMPHS OF APPLIED SCIENCE In connection with various portions of this chapter the reader will find much that is of interest in the story of chemical development in general as detailed in volume III., pp. 3-72 inclusive. Also various chapters on electricity as outlined under chapter VII. above. (p. 310). Nitrogen from the air. The quotation is from the _Engineering Supplement_ of the London _Times_, January 22, 1908. TRANSCRIBER'S NOTES Italic text is denoted by _underscores_. The oe ligature has been expanded to 'oe'. Subscripts in chemical formulas are denoted by normal numbers; for example CaC2.