One pole of the battery B' is connected with the frame of the time distributor T; the other pole connects with the different clock circuits (two in the diagram): when the centre contact C conies in contact with the first set of contact springs r, it closes the circuit of the clock-line L. The current, following the course indicated by the arrows, passes from the battery to the frame T of the time-distributor; thence to the centre con tact C into Chic contact springs r; then to the different clocks in the line L and the sentinel back to the battery B' . The same process takes place in the clock circuit LI as soon as C comes iu contact with the con tact springs 6, etc.
As electric clocks have for their object the indication of correct time, any break in the time service will mislead; hence automatic means should be provided for the immediate detection of any interruption. For this purpose Spellier devised an apparatus called the "sentinel," which gives audible notice of any trouble as soon as it appears. This sentinel (pi. 136, jig. r r) consists of a spring clockwork (A) and of an electro-magnetic escapement (A) whose magnet is in the circuit of the electric dials. The escape-wheel I; has on the front of each tooth a pin (c); the arbor of the hour-wheel h of the spring clock carries a lever (C) which is movable on the arbor, but is held spring-tight by a spring (c). The operation of the escapement is as follows: When the electric current actuates the escape ments of the electric dials in the circuit, it also actuates the escapement A and the pin c, toward which the lever C is moved by the arbor of the hour-wheel, and pushes the lever backward and passes it. Should the cur rent, however, fail to pass (on account of a broken wire, for example), the escapement A and all the clocks will cease moving, and the arbor of the spring-clock hour-wheel will carry the lever C to the contact-point d, whereupon there is closed a separate battery which rings a signal-bell and announces the pending trouble. If the sentinel escapement is made a little more sluggish in action than the escapements of the electric dials, any of the battery will first be shown at the sentinel, which will fail to operate, and the lever will then be carried to the contact-point d, and will ring the bell before the battery is sufficiently weak to affect the clocks in the circuit.
Synchronizing first attempt to use an electric current for obtaining uniform time was made by Steinheil, who for electrically cor recting ordinary clocks devised what is known as the "synchronizing" system, which has been developed by other inventors and is still employed. The clocks in line are each provided with an electromagnet and are elec trically connected with a master clock. At fixed periods, ranging from one to twenty-four hours (in the latter case at noon), there is sent by the master clock through the magnets of the clocks in line an electric current which attracts their armatures and actuates a mechanism which corrects the hands of the clocks not indicating correct time. As the subordinate clocks require the same attention and are subject to the same accidents as ordinary clocks, this system is less desirable than one purely electrical.
Clocks lUound by Electricity, or "self-winding" clocks, as they are called, are wound automatically by an electric motor, which continues to act as long as the galvanic battery operating the motor remains strong enough to furnish a sufficient current to drive the motor, and do not require the personal attention that must be given in winding spring- and weight-clocks by hand. The self-winding clock promises to become a val uable factor in the synchronizing method of electric time-distribution.
have become a popular convenience for indicating the mo ment when the sun passes the meridian of a place whose time is accepted as the standard. A staff erected at au elevated position is provided with a large ball having a hole through its centre to allow the ball to glide down the staff. The ball is held at the upper end of the staff in a fixed position by an appropriate mechanism, which is so arranged that through the action of an electromagnet the ball can be set free and glide down the staff. The electric current, which passes through the magnet of the time-ball and causes it to fall, is sent daily exactly at noon from an astronomical observatory. To mariners in seaports the time-ball has become an especially valuable means for determining the correctness of their Chro nometers.