TIME-KEEPING IN PARIS. 309 



with the electro-magnet of the clock at sixty-five seconds before the 

 end of each hour, and .reverses the operation at five seconds after the 

 end of the hour. Ten seconds after the end of the hour the first cur- 

 rent from the regulator at the Hotel de Ville automatically stops, and 

 the wires are restored to the telegraph. The clocks at the mairies, 

 being thus corrected every hour, run with very small error ; but, should 

 for any reason the error become large, or the clock stop, this is indi- 

 cated automatically by the fact that the current from the "horary cen- 

 tei*," instead of stopping precisely at twelve o'clock, continues for thirty 

 seconds. By this, the operator at once knows that his clock is wrong, 

 and can have it set right. From the other "horary centers" the num- 

 ber of lines is in no case larger than six, the lines are shorter, and the 

 apparatus accordingly simpler. 



But there is another novel and ingenious method for the distribu- 

 tion of time in use in Paris, which, though lacking in accuracy suf- 

 ficient for scientific purposes, has both convenience and economy to 

 recommend it for general uses, and for that reason has become quite 

 extensively employed in a short time. Abandoning electricity as an 

 uncertain means for moving clock-work at a distance, the inventors of 

 this system, Messrs. Popp and Resch, have accomplished the same 

 object by the use of compressed air and for this reason have called 

 their clocks " pneumatic clocks." They were exhibited at the Expo- 

 sition at Vienna in 1878, and are now widely distributed in that city. 



The essential parts of the system are three : 1. Machinery whose 

 function it is to compress the air, and to propel impulses of the same 

 every minute ; 2. Pipes led through the streets and into the houses ; 

 3. Dials provided with mechanism for receiving the pneumatic im- 

 pulses. 



1. At a central point a steam-engine drives pumps which compress 

 air to five atmospheres in a reservoir holding eight cubic metres. This 

 compressed air is sent, by means of a special regulator, into a second 

 receiver called the " distributing reservoir," where the pressure is kept 

 constant at seventh tenths of an atmosphere, or a little less a pressure 

 determined empirically to be sufficient to move the dials. The " dis- 

 tributing reservoir " is opened to transmit an impulse into the pipes 

 each minute, for about twenty seconds, by a distributing clock (Fig. 4). 

 This consists of two distinct movements. The one to the left, provided 

 with balance-wheel, counter-weights, etc., is simply an ordinary clock, 

 and indicates the hour, minute, and second, as shown in the figure. 

 The movement to the right is contrived especially for moving the dis- 

 tributing valve, R. This valve, ingeniously arranged in such a way 

 that the pressure acts only on a minimum of its surface, is inclosed in 

 a valve-box and has three orifices. The first of these puts the valve in 

 communication with the "distributing reservoir" ; the second puts it 

 in communication with the street-pipes ; and the third puts the pipes 

 in communication with the atmosphere. The first orifice is always 



