CHAP, vi.] ELECTRIC HOROLOGY. 639 



II. ELECTRIC CLOCKS PROPERLY so CALLED. 



We have seen in the book devoted to gravitation that the driving 

 power of clocks is derived either from a weight or from a spring, and 

 that the pendulum serves to regulate the motion communicated to the 

 wheels by this force. The regularity of their motion depends on that 

 of the oscillations of the pendulum, whose amplitudes should remain 

 as far as possible invariable. The motion of the pendulum is moreover 

 kept up by the action of the escapement. 



The problem sought to be solved by the inventors of electric 

 clocks is to give to the pendulum directly, and without the employ- 

 ment of a motor, or of ordinary wheels, ah impulse derived from 

 electricity, which shall keep up and regulate its motion. The following 

 are some examples of electric pendulums in which this condition is 

 realized. 



That represented in Fig. 419 is one of the oldest; it is due to an 

 ingenious and experienced clockmaker of Beauvais, M. Verite. 



The pendulum B, hung by a spring or isochronous support, carries a 

 rigid crossbar, AD, with two pegs, which move freely inside two metallic 

 bells, c and c'. These latter are suspended by very fine silver threads 

 armed with counterpoises, p and p, to a horizontal lever, whose two 

 branches are insulated in the middle by a piece of ivory. Two 

 electro -magnets, E and E', have their poles placed Apposite two arma- 

 tures of soft iron carried by the lever, and each is connected metallically 

 with the corresponding branch of the lever and also with one of the 

 poles of the battery. The other pole communicates by a wire with 

 the suspending spring of the pendulum. 



When the pendulum at rest is vertical, the pegs of the crossbar 

 AD are not in contact with either of the bells. But contact takes 

 place with one of them, say that to the right, when the pendulum is 

 started towards the right. By this contact the circuit is closed and 

 energizes the electro-magnet E', which attracts the right-hand branch 

 of the lever. The bell c' goes down, and by its weight acts on the 

 peg and gives the pendulum an impulse in a retrograde direction. 

 Through the motion thus impressed, the contact of the peg with c' 

 ceases, and the current is broken. But the pendulum, in moving to 



