Contents 



vented for transmitting and for receiving. Extremely 

 small magnets suffice. A single blade of grass forms 

 a telephonic circuit 57 



DAM, H. J. W. 



PHOTOGRAPHING THE UNSEEN 



Rontgen indebted to the researches of Faraday, 

 Clerk-Maxwell, Hertz, Lodge and Lenard The human 

 optic nerve is affected by a very small range in the waves 

 that exist in the ether. Beyond the visible spectrum 

 of common light are vibrations which have long been 

 known as heat or as photographically active Crookes 

 in a vacuous bulb produced soft light from high tension 

 electricity Lenard found that rays from a Crookes' 

 tube passed through substances opaque to common 

 light. Rontgen extended these experiments and used 

 the ravs photographically, taking pictures of the bones 

 of the hand through living flesh, and so on. .... 87 



ILES, GEORGE 



THE WIRELESS TELEGRAPH 



What may follow upon electric induction. Telegraphy 

 to a moving train. The Preece induction method: 

 its limits. Marconi's system. His precursors, Hertz, 

 Onesti, Branly and Lodge. The coherer and the 

 vertical wire form the essence of the apparatus. Wire- 

 less telegraphy at sea 109 



ILES, GEORGE 



ELECTRICITY, WHAT ITS MASTERY MEANS: 

 WITH A REVIEW AND A PROSPECT 



Electricity does all that fire ever did, does it better, 

 and performs uncounted services impossible to flame. 

 Its mastery means as great a forward stride as the 

 xi 



