194 ELECTRIC CLOCKS 



is transmitted to a train of tho usual character, but much lighter. For largo clocks, 

 Mr. Bain proposes a modification of tho slide, which shall invert tho current at each 

 oscillation, so as to have attraction as a maintaining power in both oscillations. The 

 general arrangement of the pendulum is shown in Jig. 774. B is the pendulum bob, 

 with its coil of wire, the ends of which pass up on either sido of the rod. z and c are 

 the battery plates, with their attached wires D and D'. The arrows show the course of 

 the voltaic current from tho plate c by the wire D', thence down tho penduluin rod by 

 the right-hand wire, through the coil B, up by the wire on left side of rod, then by the 

 wire c, along the slide at E, and by the wire D to the zinc plate z. When tho slide 

 E is in position, the circuit is complete, and the bob is attracted by the n polo of one 

 of the magnets, and repelled by the n' pole of the other. When the slide is displaced, 

 the attraction ceases, and the pendulum is left to tho mere action of gravity. 



Shepherd's electric clock has a remontoir escapement. There is no direct connec- 

 tion between the electric force and the pendulum, or between the pendulum and the 

 clock-train. The attractive power, derived from tho electric current, is simply em- 

 ployed to raise the same small weight to the same height; and the clock-train is 

 carried by the attractive force derived from electric currents, whose circuits are com- 

 pleted by the pendulum touching contact springs. The pendulum is thus protected 

 from the influence of change in the force of the current, or from irregular resistances 

 in the train. Fig. 775 is a perspective view of this pendulum, with batteries, s z, 

 attached, and the clock connections and those of its batteries, s z, s z, shown. The 

 electricity leaves the pendulum battery by the wire A, and returns to it by the wire F. 

 There is only one break in this circuit, namely, at E, which is a slender spring faced 

 with platinum, that is in contact with platinum on the pendulum at the extreme of its 

 right vibration, but at no other time. The wire A reaches the pendulum from tho 

 battery by the coils B, the plate c, and the frame D ; the wire F goes direct from the 

 spring E to the zinc z. From this arrangement, it happens that every time the con- 

 tact at E is completed, the iron core, of which the ends N s are visible, contained 

 within the coils B, becomes a magnet, and when the contact at E is broken, the 

 magnetism ceases. The poles N s have, therefore, a power alternately to attract and 

 to release a, which is a plate or armature of soft iron, moving on an axis, as shown 

 in the figure, and to which is attached a bar b, with a counterpoise i. We have said 

 that the office here of the electric force is merely to raise a weight ; the fall of tho 

 weight maintains the pendulum in motion. When the armature a is attracted, the 

 lever b is raised ; this raises the wire c into a horizontal position, and its other part 

 d into a vertical position ; the latter is caught and retained by the latch or detente ; so 

 that when the magnetic attraction ceases, the counterpoise i descends with the lever 

 b ; and so the armature a leaves the electro-magnet N s. But the wire d remains 

 vertical, and its other part with the small weight c remains horizontal. Now, when 

 the pendulum makes its left-hand oscillation, the point of the screw / impinges upon 

 the stem g, and carries it a little to the left : this raises the detent e, and liberates the 

 piece d c, which descends into its original position by gravity ; the small ball c adds 

 to its weight. In descending, the vertical piece c strikes against the point of tho 

 screw h, and gives a small impulse to the pendulum p. The ball c is not larger than 

 a pea, and its fall is not an eighth of an inch ; but the impact is sufficient to keep the 

 pendulum in motion ; and it is constant, being this same body falling through the 

 same space ; and is independent of any variation in tho battery power, which latter is 

 only concerned in raising the ball. The arc of the pendulum's vibration is regulated 

 by adjusting the small ball to a greater or less distance from tho centre. Provision is 

 thus made for maintaining tho pendulum in motion, and giving it an impact of con- 

 stant value. If this arrangement is in connection with a compensating mercurial 

 pendulum, extreme accuracy of time-keeping is attained. The next step is to transfer 

 the seconds thus secured to a dial or clock. The same movement of the keeper a 

 with its counterpoise i, has sometimes been made to impart motion to tho seconds 

 wheel of a clock-train ; but more commonly tho clock train is distinct, as shown in tho 

 drawing, and is carried by a special electro-magnetic arrangement, in connection with 

 separate batteries, z *, z s, the contacts of which are, however, under the control of 

 the pendulum. Insulated springs, k and I, are fixed near the top of the rod ; from k 

 n wire leads to tho silver s, of tho left-hand battery ; and from I another wire leads to 

 the zinc z, of tho right-hand battery. The other metals of the respective batteries am 

 connected by a wire with an electro-magnet within the clock, tho other end of tin- said 

 electro-magnet being connected with tho metal bed and frame of the pendulum. When, 

 therefore, the pendulum oscillates to tho right, the circuit is completed at k ; and tho 

 current of the left-hand battery circulates from s through tho wire k: and thence 

 through the metal frame and by the wire to tho clock, and so to tho zinc c. When 

 the oscillation is to the left, and I is in contact, tho right-hand battery is in actio:i, and 

 the current circulates from s, through the clock, to the metal frame, and thence rn / 

 and to the zinc z of tho battery. In one case, a voltaic current enters the clock by 



