ELECTRIC CLOCKS 



195 



the wire shown below, and leaves it by the upper wire ; and, in the other case, it 

 enters by the upper and leaves by the lower wire. There is a double set of electro- 

 magnets within the clock, showing four poles in all ; there are also two magnetised 

 steel bars, mounted see-saw fashion, with their poles alternate, and facing the four 

 electro-magnetic poles. When the current enters the clock from below or in one 

 direction, the bars oscillate this way ; when it enters from above or in the reverse 

 direction, they oscillate that way. They are both fixed at right angles to and upon 

 the same axis ; which axis carries a pair of driving pallets, that act on a scape-wheel, 

 and so the clock-train is driven. It will be seen at a glance that two or more clocks 

 may be connected in the same circuit, as readily as one ; it being merely necessary in 

 such case to modify the battery power, to correspond with the work to be done. 

 For instance, three such clocks have been going for several years at Tonbridge by 

 the same pendulum ; several are actuated in like manner at the Eoyal Observatory, 

 Greenwich. Nor is it necessary that the clocks should be in the same room with the 

 pendulum, or in the same building, or even in the same parish. All the clocks above 

 referred to, are variously distributed ; and one of the Observatory clocks is six miles 

 distant from its pendulum, being at the London Bridge Station of the South-Eastern 

 Kailway. 



In cases where it has not been found convenient to drive the clock-train, especially 

 in the case of a public one, the movement of which is heavy, great advantage has 

 been derived for regulating the oscillations of the pendulum of the large clock, by 

 means of electric currents, under the control of a standard pendulum. Mr. Jones 

 has adopted this method, and it is likely to meet with much favour. The turret- 

 clock, under this arrangement, is driven by weights in the usual way, and the time is 

 regulated by a pendulum. The bob of the pendulum is placed under a condition 

 analogous to that of Bain's (Jiff. 774), the permanent magnet, however, being attached 

 to the pendulum, and the electro-magnet fixed facing it. If currents are made to 

 circulate synchronously in the latter, by means of a standard pendulum, the oscillations 

 of the pendulum of the turret-clock are constrained to accord with those of the 

 standard, and a very perfect system of time-keeping is obtained. This is practised at 

 Liverpool ; and has been introduced at Greenwich. 



Under the above arrangements the clock is controlled by the standard pendulum 

 second by second, and the two keep time together throughout the day. There are 

 cases in which it is sufficient, and also more convenient, to correct a clock once a day 

 only by means of a telegraph-signal transmitted from a standard clock. This is 

 managed in several ways. There is a clock at the Telegraph Office in the Strand ; 

 a good regulator, adjusted to gain a second or two during the twenty-four hours, and 

 to stop at one P.M. A telegraph-signal is sent from the Eoyal Observatory precisely 

 at one, that drops a time-ball at the Strand office, which, in falling, starts the clock. 

 At Ashford, seventy-three miles from Greenwich, there is an electric clock which has 

 a gaining rate, and which is so constructed that the battery circuit is opened at one 

 o'clock by means of pins and springs attached to the movement, and the clock there- 

 fore stops. At one P.M., Greenwich mean time, a signal is sent through the Ashford 

 clock from the Eoyal Observatory, which starts it at once at true time. At the Post 

 Office, Lombard Street, there is a clock which, 

 in the course of the twenty-four hours, raises a 

 weight. At noon a telegraph signal is sent 

 from Greenwich, which passes through an 

 electro-magnet ; the latter attracts an armature 

 of soft iron and liberates the ball, which falls, 

 and in falling it encounters a crutch or lever, 

 attached to the seconds-hand, and thrusts it 

 this way or that, as the case may be ; but so 

 as to bring it to sixty seconds on the dial, and 

 thus to set the clock right. 



Intermediate between the one method of 

 sending a signal every second to regulate a 

 clock, and the other method of sending it once 

 a day, we have the following arrangement of 

 Bain's for sending it once an hour. Fig. 776 

 shows the arrangement, with part of the dial 

 removed, to show the position of the electro- 

 magnet. The armature is below ; it carries a 

 vertical stem terminating above in a fork. Its ordinary position is shown by the dotted 

 lines. The minute hand (partly removed from the cut) carries a pin on its back sur- 

 face. When the hand is near to sixty minutes, and an electric current is sent through 

 the magnet, the armature is attracted upwards and the fork takes the position shown 



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