Page:Popular Science Monthly Volume 11.djvu/191

Rh If by any mischance the ball does not so fall at noon, it is kept up to its place until 12h 5m 0s, when it is dropped. To signalize this programme, which may occasionally be necessary, a small flag marked 12h 5m will be at once hoisted, and kept flying till the ball is dropped. A ball of this size can be seen by every vessel lying at the wharves of Brooklyn and New York, either in the North or East River, and by every vessel in the bay, even beyond Quarantine, if the ordinary night-glass is employed.

At the instant of the fall their chronometers should indicate 4h 56m 1.65s (Greenwich time), and the difference between this time and what their chronometers really give is the correction to them. Daily observations of the fall of this ball will give the daily gain or loss of the chronometers; that is, their rates.

A capital advantage will be that such corrections and rates can be determined without removing the chronometer from the ship, so that a fertile source of disturbance which accompanies the carriage of the chronometer to and from the vessel is thus, in future, avoidable. To the citizens of New York and Brooklyn the ball is widely visible. It can be seen on Broadway from Grace Church nearly to the Battery, and a suitable position can be found nearly anywhere in the city from which its face can be observed.

Incidental to this programme, and as an immediate consequence of it, the means of securing an accurate agreement of clocks throughout the city is at hand. The Western Union Company will agree to control electrically other clocks in New York City and vicinity, so that they shall constantly indicate the standard time. One means of doing this is so simple that it deserves mention. Each clock to be so controlled has an attachment contrived so that when its hands arrive at the position 12h 0m a small pin is thrown out through a hole in the clock-face just in front of the minute-hand, which is thus held fast at twelve o'clock. The outer end of the hand is held fast, but the axis on which the inner end is placed keeps on turning, so that the clock-train is not interfered with. This is the mechanical arrangement. The practical working of the system is as follows: Each clock is regulated so as to gain from ten to thirty seconds daily; therefore, when its hands reach noon, it is not really noon, but lacks from ten to thirty seconds of it. The pin is protruded, and fastens the minute hand in its place till it is withdrawn by an electric signal from the regulating or motor clock, and then all the hands start together, and continue to move for twenty-four hours, gaining their ten or twenty seconds in time for a repetition of the process on the next day. This beautiful and simple device, invented by Bain, has another advantage—that of cheapness—for it requires the use of the wire from the controlling clock but for an instant each day, and, in a crowded city like New York, the expense of erecting and maintaining the necessary telegraphic wire from each clock to the controlling clock is a minimum.