of light.

Sec. 5. The X-Rays: Roentgen's discovery--Properties
of X-rays--Not homogeneous--Rutherford and M'Clung's
experiments on energy corresponding to--Barkla's
experiments on polarisation of--Their speed that of
light--Are they merely ultra-violet?--Stokes and
Wiechert's theory of independent pulsations generally
preferred--J.J. Thomson's idea of their formation--
Sutherland's and Le Bon's theories--The N-Rays--
Blondlot's discovery--Experiments cannot be repeated
outside France--Gutton and Mascart's confirmation--
Negative experiments prove nothing--Supposed
wave-length of N-rays.

Sec. 6. The Ether and Gravitation: Descartes'
and Newton's ideas on gravitation--Its speed and
other extraordinary characteristics--Lesage's
hypothesis--Cremieux' experiments with drops of
liquids--Hypothesis of ether insufficient.

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.

CHAPTER VIII

THE CONDUCTIVITY OF GASES AND THE IONS

Sec. 1. The Conductivity of Gases: Relations of matter to
ether cardinal problem--Conductivity of gases at first
misapprehended--Erman's forgotten researches--Giese
first notices phenomenon--Experiment with X-rays--
J.J. Thomson's interpretation--Ionized gas not obedient
to Ohm's law--Discharge of char