CHAPTER VI

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WAVES AND RIPPLES IN THE ÆTHER.

The experiments of Heinrich Hertz—Electric radiation—Lecture apparatus for producing and detecting electric radiation—Electric transparency and opacity—Why this difference—The reflection of electric radiation—The refraction of electric rays—An electric prism and an electric lens—The electric refractive index—Interference of electric rays—The velocity of electric radiations identical with that of light—Dark heat rays—Actinic or photographic rays—The cause of colour—The frequency of light waves—The classification of electric or æther waves—The gamut of æther waves—The eye an æther-wave detector of limited power—The electro-magnetic theory of light—Artificial production of light—Use of Hertz waves in wireless telegraphy—Marconi’s methods—Marconi’s aerial and wave-detector—The Morse alphabet—How a wireless message is sent—The tuning of wireless stations—Communication between ships and shore—The velocity of wireless waves—Conclusion 232

APPENDIX 287

INDEX 293

USEFUL MEMORANDA.

One statute mile is 5280 feet. One nautical mile is 6086 feet = 1¹⁄₆ statute mile. A knot is a speed of 1 nautical mile per hour.

Hence the following rules:—

To convert Knots to miles per hour—multiply by 1¹⁄₆. Miles per hour to knots—multiply by ⁶⁄₇. Feet per second to miles per hour—multiply by ²⁄₃. ⁄ Feet per second to knots—multiply by ⁶⁄₁₀. Knots to feet per minute—multiply by 100.

WAVES AND RIPPLES IN WATER, AIR, AND ÆTHER.

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