THE importance of precise and uniform time throughout Paris becoming ever and continually more appreciated, the Municipality have taken the matter in hand, and have established a system of what they call “horary centres.” These horary centres really consist of standard clocks, erected in different places, and controlled by electricity from the Paris Observatory. Moreover each standard clock is furnished with additional electrical work of its own, which enables it to send out an hourly current and control other clocks in its neighbourhood, placed in circuit with it. The advantage of this arrangement over any system of electrical dials is apparent, for with the latter any mischance or practical joke with the wires would cause the whole city to be misled or completely deprived of time. The problem, as put by Leverrier, and as it has been practically solved by M. Breguet, was this:—To keep correct the hour given by various regulators distributed in the city by means of an electric current sent from the Observatory. If the current, in consequence of any accident, fails, the regulators continue to work, with a very slight advance, without the electric correction. The wires have their centre at the Observatory, where there is an astronomical regulator on the first floor. This instrument is maintained at the exact time indicated by the astronomical observations, by means of an arrangement which obviates the stopping of the pendulum and changing its length. At the bottom of Fig. 1 is a box C, in which may be placed small weights. The weights are of such a shape that it is easy with suitable pincers to put them in or take them out without touching the clock or disturbing anything. The addition of a weight makes the regulator go faster; its withdrawal retards it. At the upper part of the pendulum is seen the apparatus by which the currents are transmitted; it is in duplicate, because the pendulum beats seconds, and it is desired to send the current every second. Each apparatus is composed of three identical pieces; three small levers are placed side by side, pivoted at their farthest ends. Their end i is raised by the arm v carried by the pendulum at each of its oscillations. During all the time which this contact lasts, the current of a battery passes by the suspension of the pendulum to the arm which carries the three screws and the three levers which conduct it to the line. With a single leverthere would be danger of interruptions by a grain of dust; with three, contact and transmission of the current are absolutely assured. From the Observatory two wires set out; no use is made of the return earth current. The wires are entirely in the drains, like those of the Telephone Company. Fig. 3 shows these two circuits, each of which is attached to the Observatory by its two extremities. These lines pass by a series of points and traverse the regulators, of which we shall now speak, and which are called horary centres. The pendulum of each regulator (Fig. 2) presents at its lower part a piece of soft iron, which in the oscillations of the pendulum is brought in front of the poles of two electro-magnets in succession. The transmission of the current into these electro-magnets tends to retard a little the movements of the pendulum, and causes each to be perfectly synchronous with that of the Observatory. The regulators of the horary centres show the second; they are placed in the street, and consequently in view of the passers-by, who may thus compare their watches. Watchmakers may also thus obtain the exact time without making a journey to the Observatory. They are placed in several prominent buildings in various convenient centres.
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