Identifier: practicaltelepho00pool (find matches)
Title: The practical telephone handbook and guide to the telephonic exchange
Year: 1906 (1900s)
Authors: Poole, Joseph
Subjects: Telephone
Publisher: New York, Macmillan Co.
Contributing Library: Northeastern University, Snell Library
Digitizing Sponsor: Boston Library Consortium Member Libraries

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ent flowing will be given in amperes. If brepresents ohms, e volts, and c amperes, then the relation between the three will be represented by c = — , or e = cb, or Rb = - ; so that, given any two of these quantities, it is easy to find the third. This law applies equally to a portion of acircuit as well as to the whole; so that if we know the P.D.between any two points of a closed circuit, and the strength 8 PRACTICAL TELEPHONE HANDBOOK of the current passing, we can at once determine the re-sistance between the two points. Medium of Propagation.—Whatever may be the real natureof the electric current which causes the effects produced, itis now generally admitted that the medium through whichthe cause of the current, or the energy of the current, is pro-pagated, is not in the conductor itself, but in the insulatingmedium surrounding the conducting circuit. In other words,the energy absorbed and again given out by a generator ofE.M.F. is transmitted through the ether surrounding the
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Fig. 3 conductor, and is from that impressed upon the conductor, soas to produce the various effects in the form of heat or work.The conductor merely acts as a guide to the electric waves,keeping them directed along the circuit instead of allowingthem to spread in all directions through the ether (as happensin wireless telegraphy), and so become rapidly dissipated. Magnetism.—Magnetic Lines of Force.—The reader will befamiliar with the beautiful curves in which iron tilings setthemselves when sprinkled over a card covering a magnet,as shown in Fig. 3, where the magnet is shown above the card.At the poles, or points of greatest magnetic density, the linesare clustered together, and they spre^d out from these points INTRODUCTORY 9 in symmetrical curves. These curves represent only sectionsof the magnetic field surrounding the magnet, and show thedirection in which the magnetic force acts, and in which smallmagnetic needles free to move would set themselves. A pieceof soft iron in th

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