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

E. & F. N. Spon, 1868 - Electric measurements - 175 pages

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Page 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...
Page 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.
Page 144 - Ib. is 1002•4 ohms at 60° Fahr. No. 16 copper wire of good quality has a resistance of about 19 ohms. The resistance of a statute mile of pure copper weighing w Ibs., is ohms at 60° Fahr.
Page 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...
Page 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
Page 108 - Measurement,' p. 108, by L. Clarke). From this table it will be observed, that the strength of a Smee's cell decreases during its working ; this occurs very quickly after the current commences, because the internal resistance is increased...
Page 94 - Two forces are now acting on the needle and balancing each other, viz., the directive force of the earth's magnetism, and the deflecting force of the current flowing through the coil. At this moment, the strength of the current is proportional to the sine of the angle through which the coil has been turned. The values of the sines may be obtained from a table of natural sines.
Page 108 - Davy) 76 Chloride silver 62 Chloride lead 30 When connected on short circuit, the electro-motive force of several of the batteries, especially Smee's and Wollaston's, will fall off 50 per cent, or more, owing to ,the formation of hydrogen on the negative plate. Grove's and Daniell's do not so fall off, because the hydrogen is reduced by the nitric acid in one case and by the oxygen in the other.
Page viii - Before proceeding farther it is necessary to have a clear conception of the meaning of the term
Page 154 - VJ v. , The strain is greater at the point of suspension than at the lowest point of the span, by a quantity (equal to the weight of a length of wire of the same height as the versine) which maybe neglected in practice. Calling I the length of the span in feet, w the weight in cwts. of one statute mile, v the versine in inches, and s the strain in Ibs., PX w Strain = ^ 43 xy Ibs.