Page:Popular Science Monthly Volume 22.djvu/348

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The actual interval during which the Greenwich as well as the provincial wires on which the time-signal is distributed are kept in circuit being only twenty seconds, the chance of interruption from contact currents is reduced to a minimum.

The batteries in use are large Leclanché cells, and the power is distributed as follows:

Copper or "time"
Zinc or "preliminary"
Long lines 80 cells. 60 cells.
Medium lines 60 " 45 "
Short lines 40 " 30 "
Metropolitan lines 40 " . . "

The Greenwich signal, thus distributed by the chronopher, goes to all parts of the kingdom, and affects receiving instruments provided for the purpose. These are of various kinds; ordinary telegraphic sounders, electric bells, and galvanometers have been used with success to note the arrival of the signal. The current has also been made to drop time-balls on the tops of buildings, to expose a model time ball to view, and to fire guns.

To test the accuracy of the signals, experiment has been made by returning a wire to Greenwich from the chronopher, and comparing the signal received on this wire with the signal sent from the observatory; no difference could be perceived between the indications of two galvanometers placed side by side showing the passage of both currents. The signals were thus shown to be entirely reliable. But it does not seem likely that the chronopher will be introduced elsewhere, because simpler means have been devised for splitting up the current and distributing the signals.

The whole system is under the control of the Post-Office Department. They own the wires—which, except in London, are the ordinary telegraph-wires and therefore contract to keep them in order, to clear them each day at the signal-times, and to deliver at these times the Greenwich signal. Maintenance of lines and apparatus not the property of the department is undertaken by the department for any period not less than one year at specified rates. A simple form of agreement has been prepared, which every renter is required to sign. This agreement, as a rule, is for not less than three years, and is terminable at three months' notice given previous to the end of the fixed term, or, failing such notice, on payment of such sum as the department may accept instead. But where the expense of construction is considerable, the term must not be less than from five to seven years, the latter period being stipulated when the proposed line is in an outlying district and would be specially provided for a single renter, and when it is not probable that there would be other renters.

The annual charges for the use of wires and apparatus are as follows: