CHAP, vi.] ELECTRIC HOROLOGY. 641 



of the pendulum. During that part of the oscillation which takes 

 place to the left, the screw touches the weight p, the circuit is 

 closed, the armature attracted, and the branch R of the lever ceases 

 to sustain the band and weight, which then acts on the screw, and in 

 consequence on the pendulum, so as to give it a retrograde im- 

 pulse. Then the contact ceases, the circuit is opened, the armature 

 takes its original position, and the weight ceases to act. Two screws, 

 v and v', limit, on the other hand, the course of the branch L of 

 the lever. Hence it is the action of a constant weight, which at 

 each oscillation maintains the motions of the pendulum. 



Robert Houdin's electric clock is represented in Fig. 421. The 

 suspending spring of the pendulum P is in communication at o with 

 the positive pole of the battery. It is provided with two curved arms, 

 B and B', which alternately come into contact with two spring bands, 

 and so close the circuit, first with the electro-magnet E, and then with 

 the electro-magnet E'. Suppose the oscillation of the pendulum 

 begins on the right side of the figure, and the contact is then made 

 by the arm B. The current following the wires in the direction 

 marked by the arrows passes by E' ; the left branch of the armature 

 AA', being attracted, raises the spring which 'acts by means of the rods 

 t', I, and a catch on a ratchet-wheel, and makes it advance one tooth. 

 The same motion raises the little mass /, and draws up the catch c 

 below the spring, which is thus stopped, while the right-hand spring 

 is disengaged from the catch c, and is enabled to act by its weight 

 during the retrograde motion of the pendulum. Then the contact 

 ceases, the current is interrupted, the left hand armature ceases to be 

 attracted, the rod t' is lowered, and drives the upper corresponding 

 catch over the next tooth of the ratchet-wheel. 



The motion of the bob towards the left brings B' into contact with 

 the left-hand spring. The current circulates through the electro- 

 magnet E', the armature on the right is attracted, and the same motions 

 which we have just described take place on the opposite side, so that 

 it is now the left-hand spring which, when disengaged, acts by its 

 elasticity and its weight on the arm B' of the pendulum, and the catch 

 r is drawn in its turn over one tooth of the ratchet-wheel. Two 

 counterpoises, e e, which can be set at different distances on the spring 

 bands, are the means of regulating the action of these springs, and, 

 consequently, the motion of the pendulum itself. 



T T 



