Telegraphy

Telegraphy

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 edition. Excerpt: ...It is that if two conducting bodies lie against each other in loose contact, and a current of electricity flows through them, there will be resistance at the point of contact, and their vibrations will vary this resistance in exact ratio to the cause producing the vibrations. Metals and all conducting substances are subject to this effect, but carbon, probably because it is inoxidisable, is the best material, and although strenuous efforts have been made to produce a telephone transmitter without using carbon, no other material has been found to answer as well. 'Pencil' Microphone 249 This effect is so sensitive that Professor Hughes was able with his microphone to render evident sounds that otherwise were absolutely inaudible. One of the best known forms in which this principle is introduced is the Gower-Bell telephone, a modification of which has been extensively employed by the British Post Office. On a thin dry pinewood board are fixed two angular straps of thin copper plate, ss' (fig. 154), and a carbon block, c. On each copper strap are fixed four carbon blocks, cM c2, c3) c4. Holes are drilled in the sides of all these blocks, and eight carbon pencils, with their ends turned down, rest lightly in these holes in the positions shown, and there make loose and imperfect contact. This microphone replaces in fig. 153 the carbon transmitter of Edison (t). The actual resistance of the carbon contact varies from 8" to 10." The effect of sonorous vibrations is the same. Secondary currents are formed and speech is reproduced. Fig. 155 shows the later system of connections of the Gower-Bell telephone. c is the induction coil, the primary and secondary wires being for the sake of clearness shown distinct from each other. The primary wire has...show more

Product details

  • Paperback | 124 pages
  • 189 x 246 x 7mm | 236g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 123659388X
  • 9781236593887