Knight's Mechanical Encyclopedia, T., Time-sig′nal.

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19th-Century American

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Time-sig′nal.

A means of indicating the local time at an observatory to observers at one or several distant points.

Dropping a ball (time-ball) at a fixed hour, 1 o'clock, P. M., or mean noon daily, has long been in use in maritime cities and observatories. This serves as a means of regulating or ascertaining the rate of clocks or chronometers at all points where the falling of the ball is visible.

The electro-magnetic telegraph has been used for operating time-signals at much greater distances; thus, the Greenwich time is indicated at Liverpool and other cities in England by the dropping of a ball by means of an electric circuit operated from Greenwich, the circuit being automatically closed at one o'clock. The ball is dropped through the intervention of a series of levers, to one of which, acting as a detent, the armature of an electro-magnet, made so by the closing of the circuit, is attached. When this is attracted by closing the circuit, the detent is withdrawn and the ball falls.

By galvanometers placed in the circuits of the time wire to Liverpool, and the return wire, it was ascertained that the time elapsing between the receipt of the current in London and the discharge of the ball in Liverpool was 1 1/20 of a second; of this 2/20 were occupied by the automatic circuit-closer, 4/20 by the ball-trigger mechanism, leaving 5/20 of a second for the passage of the current by the underground wire.

By means of an improved arrangement devised by Mr. Varley for connecting the observatory at the Cape of Good Hope with time-balls at Simonstown and Port Elizabeth, the time elapsing between the passage of the current at Capetown and that announcing the falling of the ball at Port Elizabeth, 500 miles distant, is found to be but 1/15 of a second.

1877.

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Knight's Mechanical Encyclopedia
Knight, Ed.

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Time-sig′nal.

Knight's Mechanical Encyclopedia Knight, Ed.

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Time-sig′nal.

Knight's Mechanical Encyclopedia
Knight, Ed.