368 



NATURE 



\_Feb. 17, 1 88 1 



by means of an arrangement which obviates the stopping 

 of the pendulum and changing its length. At the bottom 

 of Fig. I ia 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 / 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 sus] ension of the pendulum to 

 the arm which carries the three screws and the three levers 

 which conduct it totheline. With a single leverthere «ould 

 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 



Fig, I. — Regulator of Paris Observatory. 



which is attached to the Observatory by its two ex- 

 tremities. These hnes 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 the^e electro-magnets 

 tends to retard a little the movements of the pendulum, 

 and causes each to be perfectly synchronous with that of 

 the Cbservatory. The regulators of the horary centres 

 show the second ; they are placed in the street, and con- 

 sequently 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. 



Why these regulators are called horary centres is 

 explained thus : upon the circuit of horary centres 

 spoken of above, and which the accompanying plan 

 (Fig. 3) indicates by a black line, is grafted another 

 accessory, called the transmission of the hour. Each 

 regulator of the main circuit is itself the centre of a 

 less extensive network of wires, which transmit the hour 

 to the public clocks. For this second service no unique 



system has been adopted, and uniformity has not been 

 aimed at. Several of the principal watchmakers of 

 Paris, inventors each of a special method of transmitting 

 the hour, are authoriaed to apply it to the clocks of which 

 they have the care, by borrowing the hour and the current 

 from the nearest horary centre. The most interesting 

 horary centre is that installed at the Hotel de Ville (at 

 present the Tuileries), and which radiates to the twenty 

 inairies of Paris. The city has a telegraphic communi- 

 cation which places the Prefecture of the Seine in connec- 

 tion with the twenty mairies. The wires of this system tre 

 interrupted about two minutes every hour to place the 

 clock of each mairie into agreement with the regulator 

 (horary centre) of the Hotel de Ville as follows. Beside the 

 regulator are placed twenty relays, into which it sends 

 every hour a current, which cuts off the Ime from the tele- 

 graph ; this commutation is made 100 seconds before the 

 hour. The same regulator, about twelve seconds before 

 the hour, sends the current from a second battery along 



Fig. 2 — Regulator of the Horary Centre. 



the lines ; it interrupts it at the hour precisely. Ten 

 seconds after the hcur the relays are restored to their 

 nonnal position by the suppression of the first current ; 

 that is to say, the lines are restored to the telegraph. 



On the other hand sixty-five seconds before the hour 

 each uiaiiie clock makes its commutation, i.e. cuts off the 

 line from the telegraph and connects it » ith the electro- 

 magnet of the clock. And five seconds after the hour it 

 makes the inverse commutation and restores the line to 

 the telegraph five seconds before the resumption of the 

 line by the telegraph at the hon.ry centre of the Tuillcries. 

 As the clocks are thus regulated every hour their errors 

 are extremely small. If however a clock gets suddenly 

 out of order or stops, what happens ? The current of 

 the horary centre is sent into the telegraph of the mairie 

 for thirty seconds continuously ; this abnormal fact an- 

 nounces at once to the telegraphist that the clock is out 

 of order, and he may give orders to have it set right. 



In the other horary centres the organisation is less 



