[Electric engineering.] . actually pass through it,and it is at the same time entirely disconnected from thehigh-pressure dynamo leads. 14, Electrostatic Voltmeters.—-There is one kind ofvoltmeter that is sometimes used, especially for high-pres-sure alternating-current work, that differs considerably fromthe instruments so far described, both as to its constructionand principle of operation. This is the electrostatic volt-meter. It depends for its action on the principle that twobodies carrying similar static charges repel each other andthose carrying unlike charges attract each other. Fig. 1
[Electric engineering.] . actually pass through it,and it is at the same time entirely disconnected from thehigh-pressure dynamo leads. 14, Electrostatic Voltmeters.—-There is one kind ofvoltmeter that is sometimes used, especially for high-pres-sure alternating-current work, that differs considerably fromthe instruments so far described, both as to its constructionand principle of operation. This is the electrostatic volt-meter. It depends for its action on the principle that twobodies carrying similar static charges repel each other andthose carrying unlike charges attract each other. Fig. 19shows the construction of the Stanley electrostatic volt-meter. £, B and C, C are fixed plates mounted on a hard-rubber base. These plates are covered with a hard-rubbercovering H to prevent the charge from leaking off, also to 16 ELECTRIC LIGHTING. 17 obviate any danger of short-circuiting between the is a movable aluminum vane, to which is attached thepointer, the movement of which is counterbalanced by the. Fig. 19. spiral spring S. The fixed plates B, B and the movablevane A are connected together and form one pole of theinstrument. The fixed plates C, C are connected 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
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