TIME-KEEPING IN PARIS. 307 



circuit of the observatory clock. The operation is as follows : The 

 secondary clocks are kept running with :t very small gaining rate. At 

 each vibration of the pendulum of the observatory clock the circuit 

 is closed, and a current passes from a battery of six Daniell cells and 

 magnetizes one of the electro-magnets at the foot of the pendulum of 

 each secondary clock, which, attracting the piece of soft iron, retards 

 its motion. The adjustment is delicately made, so that the retardation 

 is just sufficient to keep the secondary clocks beating synchronously 

 with the observatory clock. 



This system, in Paris the device of M. Breguet, is a modification 

 of the Jones system, which is considered by scientists the best ever 

 invented for regulating clocks at a distance from the standard clock. 

 Its main advantage lies in the fact that by no disaster to the wire of 

 the circuit or to the regulator of the system can the secondary clocks 

 be stopped. Should, by any accident, the wire be broken or the ob- 

 servatory clock stopped, the secondary clocks move right on, only 

 slightly too fast ; whereas, in any system of dials which are driven by 

 a standard clock, any such mishap must of necessity stop the dials, 

 whereby those depending upon them for time are misled, if not en- 

 tirely deprived of time. In point of accuracy the results in this sys- 

 tem are indeed all that could be desired, the error of the secondary 

 clocks being kept less than one tenth of a second ; but, because the 

 secondary clocks must be fine time-keepers, the system is quite expen- 

 sive. The estimated cost of each of these clocks is from 2,400 to 2,500 

 francs, or from 1480 to $500. On the two circuits, each terminating 

 at both ends at the Observatory of Paris, there are distributed thirteen 

 clocks, the farthest being at a distance of seven and a half kilometres, 

 or nearly four and a half miles from the observatory. The clocks are 

 furnished with second-hands, and are placed so that they can be easily 

 seen from the street, and usually in prominent positions. The system 

 is entirely under municipal management and has been in successful 

 operation for about four years. 



But the system thus far described is the basis of a much wider dis- 

 tribution of accurate time ; for each of the secondary clocks is itself 

 provided with apparatus, by means of which it sends a signal every 

 hour to clocks placed on special circuits and to the public clocks of 

 the city. For this reason the secondary clocks have come to be known 

 as "horary centers." The methods employed for the distribution of 

 the hourly signals from the " horary centers " are not uniform, nor are 

 they of equal importance or extension ; some of the principal watch- 

 makers have invented methods of their own for special services, which 

 are not of general interest, but the system which radiates from the 

 "horary center" at the Hotel de Ville (at present the Tuileries) to the 

 twenty mairies of Paris is worthy of mention here both on account 

 of its importance and ingenuity. There is a system of telegraph- 

 wires connecting all the mairies of the city with the Prefecture of 



