[Electric engineering.] . ted togetherand form the other pole. When the voltmeter is connected §17 ELECTRIC LIGHTING. 17 to the circuit, B and A being charged alike will repel eachother, while at the same time C and A will attract eachother, with the result that the vane is deflected an amountdepending on the pressure of the circuit. Two plug recep-tacles T, T are provided on the instrument, in addition tothe regular terminals, so that it may be compared at any-time with a standard instrument. The movement of theneedle is damped or steadied by the vanes F moving in thepartially closed boxes D.
[Electric engineering.] . ted togetherand form the other pole. When the voltmeter is connected §17 ELECTRIC LIGHTING. 17 to the circuit, B and A being charged alike will repel eachother, while at the same time C and A will attract eachother, with the result that the vane is deflected an amountdepending on the pressure of the circuit. Two plug recep-tacles T, T are provided on the instrument, in addition tothe regular terminals, so that it may be compared at any-time with a standard instrument. The movement of theneedle is damped or steadied by the vanes F moving in thepartially closed boxes D. Other types of electrostatic instruments are made, butthey all work on about the same principle. They do not,of course, require any current for their operation and canbe connected across high-pressure lines without the inter-vention of a potential transformer. 15. Voltmeter Switches and Connections.—It has already been stated that it is customary to make one volt-meter answer for several dynamos or circuits by using a. Fig. 20. tn d voltmeter switch or plug. Fig. 20 shows one of the simplestforms of switch used for this purpose. This is suitable fortwo dynamos, and its method of operation is obvious from thefigure. The voltmeter is connected to terminals 1 and 2y 18 ELECTRIC LIGHTING. 17 and the dynamos A, B to 3 and 6, 4 and 5. Connection ismade to the terminals 3, 4, 5, 6 by means of the springcontact pieces c, d that are attached to the insulatingcross-arm F and rub on the arcs 1 and 2. In position G,machine A is connected to the voltmeter, and in position H, 29 l Q2 M/ V 02 .& V 02 .f&
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