CHAPTER VII.
WIRELESS TELEGRAPHY Sec.1.Histories of wireless telegraphy already written, and difficulties of the subject.
Sec.2.Two systems: that which uses the material media (earth, air, or water), and that which employs ether only.
Sec.3.Use of earth as return wire by Steinheil -- Morse's experiments with water of canal--Seine used as return wire during siege of Paris--Johnson and Melhuish's Indian experiments--Preece's telegraph over Bristol Channel--He welcomes Marconi.
Sec.4.Early attempts at transmission of messages through ether--Experiments of Rathenau and others.
Sec.5.Forerunners of ether telegraphy: Clerk Maxwell and Hertz--Dolbear, Hughes, and Graham Bell.
Sec.6.Telegraphy by Hertzian waves first suggested by Threlfall--Crookes', Tesla's, Lodge's, Rutherford's, and Popoff's contributions--Marconi first makes it practicable.
Sec.7.The receiver in wireless telegraphy--Varley's, Calzecchi--Onesti's, and Branly's researches-- Explanation of coherer still obscure.
Sec.8.Wireless telegraphy enters the commercial stage-- Defect of Marconi's system--Braun's, Armstrong's, Lee de Forest's, and Fessenden's systems make use of earth-- Hertz and Marconi entitled to foremost place among discoverers..