Telegraphy

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Longmans, Green, 1891 - Telegraph - 396 pages
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Page 261 - The twist-test will be made as follows: The wire will be gripped by two vises, one of which will be made to revolve at a speed not exceeding one revolution per second. The twists thus given to the wire will be reckoned by means of an ink mark which forms a spiral on the wire during torsion, the full number of twists to be visible between the vises.
Page 130 - ... necessarily adheres to them. Rain, fog, dew, and mist affect it. Lines exposed to the spray of the sea or the smoke of manufactories are peculiarly liable to this variation. Other causes also introduce irregularities which interfere with the constancy of a line. The wires are continually subject to accidents of various kinds, many of which tend to produce variable resistance. Now what effect has this variation of the resistance of the line-wire upon duplex working, and how is it provided for?...
Page 123 - B works, so that the marks, whether made by the received line current or by the preponderating compensation current, are practically the same. We have shown in the diagram that the same poles of the battery are to line, and that therefore the line currents flow in opposite directions ; but the...
Page 123 - ... line, and the currents flow in the same direction. If the current from B flows in the same direction as that from A, the effect, when the two stations work simultaneously, is not to weaken the resultant current, but to strengthen it, and therefore to produce a preponderance of the current in wire I over that in wire r of relay E, and, consequently, to register signals ; but in this case the marks made at A, when both stations are working simultaneously, are not made by the preponderance of the...
Page 121 - ... equal the polarity induced by the one current must be exactly neutralised by that induced by the other current, for the effects are equal and opposite, and there will be no magnetism excited. Thus, as long as the two circuits are intact, the currents which flow...
Page 36 - ... contact is ensured. The last zinc and the last copper are connected to brass terminals, which become respectively the negative and positive poles of the battery. Nothing but clean water (hard water should, if possible, be avoided) is poured into the zinc division, but sufficient is added to bring it up to within about a quarter of an inch of the top of the zinc plate. The battery at the end of about twenty-four hours will be found to be in working order, the sulphate having dissolved in the copper...
Page 129 - Thus it happens that the resistance of an aerial line is constantly varying. The longer the line the greater must be the extent of this variation. The amount of variation depends essentially upon the nature and age of the line and the character of the country through which the line passes. The resistance of some lines varies in bad weather as much as 50 per cent, in one day, but remains constant in fine weather. Short lines, as a rule, are little disturbed by variations of short duration, but long...
Page 128 - B be connected together by an aerial wire, supported at intervals of about 100 yards upon earthenware insulators, then the current which arrives at B from A must necessarily be less than that which leaves A, because at each pole a small portion of the current escapes or leaks to earth. No earthenware support is an absolute insulator. Moisture is deposited upon its surface. The amount of this moisture continually varies, and the resistance of the insulator to the leakage of the current varies with...
Page 197 - Rv to prolong the effect of the compensating current from the condenser. G is a differential galvanometer, used for testing, and for facilitating adjustment and balancing. Q is a switch for putting the line to earth, either for balancing, or for any other purpose. There is on the earth wire leading from Q a. resistance coil, rv equalling approximately the resistance of the whole battery, 3.3 Elt and the res1stance s. The connections shown in Fig. 321, are for an ' up
Page ii - Magnetism, y. 6d. Maxwell's Theory of Heat, y. 6d. Merrifield's Technical Arithmetic, y. 6d. Key, y. 6d. Miller's Inorganic Chemistry, y. 6d. Shelley's Workshop Appliances, y. 6d. Watson's Plane &= Solid Geometry, y.

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