An Elementary Treatise on Electrical Measurement: For the Use of Telegraph Inspectors and Operators

E. & F. N. Spon, 1868 - 175 páginas

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Página 154 - T .WJ .lnnr ohms. STRAIN OF SUSPENDED WIRES.* — The ordinary dip of line wires, for a span of 80 yards, is about 18 inches in mild weather ; this gives with No. 8 wire a strain of 420 Ibs., its breaking weight being about 1,300 Ibs. — (Culley.) The strain varies directly as the weight of the wire, and inversely as the dip or versine ; it increases as the square of the span if the dip be constant ; but to preserve a given strain the dip or versine must increase as the square of the span, or, L...
Página 60 - Now unplug the resistance-coils which are in circuit with the battery until the deflection of the needle is reduced to its original amount, and the resistances unplugged will be equal to the internal resistance of the battery. For example, assuming the resistance of the half coil to be ninety-nine ohms, and that of the shunt wire one ohm, the joint resistance of the two 'circuits will be : Galvanometer x shunt m 99^=0.90 ohm.
Página 148 - The resistance of gutta•percha diminishes as the temperature increases ; the rate of decrease is as follows : — Let R = resistance at the higher temperature ; r = resistance at the lower temperature ; t = the difference of temperature in degrees Fahr., — then log of R = log r — t log 0•9399, and log of r = log R + / log 0•9399.
Página 63 - D, and unplug resistance until a convenient deflection is obtained, say 15°; note the sum of the resistances in circuit, including that of the battery, galvanometer, resistance coil, and connecting wires; now change the cell for another, and by unplugging the resistance coils bring the needle again to the same deflection, 15°: having again found the total resistance in circuit, the relative electromotive forces of the two cells will be directly proportional to these resistances.
Página 44 - ... heat, or thermal unit, in the United States and Britain, the quantity of heat which corresponds to 1° Fahr, in the temperature of 1 Ib. of pure water at about 39° Fahr. ; in France, the heat required to raise a gramme of pure water at about 3.94° C., 1° C. — In electricity the unit of quantity is that quantity of electricity which with an electro-motive force of one volt will flow through a resistance...
Página 103 - E'; join them up successively in circuit with the same galvanometer, and by varying the resistance, cause them both to give the same deflection ; their forces will then be in direct proportion to the total resistances in circuit in each case, or t>f E' = EX 5 A where R represents the resistance with E (including that of battery, galvanometer, and the adjustable resistance) and R
Página 142 - COPPER. The specific gravity of copper wire, according to the best authorities, is about 8.899. One cubic foot weighs about 550 pounds. One cubic inch weighs 0.32 pound. The ordinary breaking weight of copper wire is about 17 tons per square inch, varying greatly, however, according to the size and degree of hardness. The weight per nautical mile of any copper wire is about - pounds, d being the diameter in mils.
Página 142 - Ibs. A mile of No. 16 wire weighs in practice from 63 to 66 Ibs. The resistance per statute mile of any pure copper wire is ^^Jr-* ohms at 60° Fahr.
Página 60 - Connect the battery and a set of resistance-coils in circuit between the terminals A and D, and insert plugs in the resistance coils so that they give no resistance; insert plugs at A and C, and also both the shunt plugs at A and D. The battery current will now flow through...

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