TIME-KEEPING IN PARIS. 



3" 



ments is furnished by the compressed air, which automatically lifts 



the pistons in the cylinders, C, at the end of each minute. The pistons 

 move the levers \\ and A ; the first of these, B, winds up the counter- 

 weights as much as they have fallen during the preceding minute ; tin: 

 second, A, imparts motion to the slide-valve. 



2. The impulse given by the clock-work is distributed through the 

 city by means of pipes laid like ordinary Lias-pipes. In the streets 

 the pipes are of iron, and have a diameter of twenty-seven millimetres 

 (about one inch) ; but in the houses the pipes are of lead, and of dif- 

 ferent sizes the diameters being fifteen, six, or three millimetres 

 (practically one half, one quarter, or one eighth of an inch), depend- 

 ing on the number and size of the dials to be operated. These pipes 

 are entirely hidden from view, and in no way interfere with the ap- 

 pearance of the dials. 



3. The mechanism of each dial, whatever the size, is shown in essen- 

 tial part in Fig. 5. A 

 leather or rubber flap, 

 seen in the cylinder, re- 

 ceives the impulse as it 

 comes from the pipe and 

 moves a piston, which 

 acts upon a lever -arm 

 arranged by simple con- 

 nections to move the 

 minute-hand one space 

 forward. The ordinary 

 clock-gearing (not shown 

 in the figure) secures the 

 proper motion for the 

 hour-hand. This part of 

 the apparatus can be in- 

 closed in any case as plain or as ornamental as desired. The cases 

 are made in all the designs and sizes of ordinary clocks, and appear 

 precisely like them, except that the minute-hands jump suddenly over 

 one space at the end of each minute, and remain stationary during the 

 minute, instead of moving gradually over the space. 



All the machinery of the system is in duplicate, for use when repairs 

 are needed. Delicate manometers indicate the pressure at all times, 

 and the most approved electric apparatus is used to indicate the par- 

 ticular point at which a defect has occurred. A skilled engineer is on 

 the watch at all times. Provision is also made so that, in case of any 

 interruption in the regulator, the dials may be run by hand. Accuracy 

 of time is secured by daily comparison with the observatory clock. 



Excellent as the system is for general uses, the pneumatic dials can 

 not be used for accurate time-work, because it requires in the extreme 

 case, namely, for a distance of twenty thousand metres, at least ten 



Fig. 5. Mechanism op a Pneumatic Dial. 



