NATURE 



{July 8, 1880 



PNE i'.UA TIC CL OCKS 



TO distribute the time witli accuracy and unifonnity in 

 a large city is a problem of great utility and extreme 

 importance. This problem has been all but completely 

 solved by the pneumatic clocks erected since March last 

 in the principal streets of Paris and among a considerable 

 number of subscribers, who, for a halfpenny a day, receive 



the time from the observatory cve>y minute without wind- 

 ing up or any care on their part. The details of the 

 system established in Paris we take from an article by 

 M. E. Hospitaller in a recent number of La Witiirc. 

 The system consists of (i) a central station where the 

 compressed air is produced and sent every minute through 

 the system of tubes ; (2) a distributing system of tubes 

 with ramifications to streets and houses; (3) a series of 



uting Clock of Compressed Air. 



dials with pneumatic receivers established in the public 

 streets and in private buildings. 



At the central works a steam-engine sets in motion two 

 pumps, which compress air into a large reservoir of about 

 eight cubic metres, at a pressure of five atmospheres. 

 This compressed air, by means of a special regula- 

 tor, is transmitted to a second chamber called the dis- 

 tributing reservoir, where the pressure is kept at seven- 

 tenths of an atmosphere by means of a simple automatic 

 apparatus. This reservoir is put into communication 

 every minute with the main distributing pipes for twenty 

 seconds by means of a distributing clock shown in Fig. I. 

 The distributing clock comprises two quite distinct move- 

 ments : the left movement is intended to set the clock 

 going in the ordinary manner ; the right movement is 

 specially intended to work the distributing valve R. 

 The seconds-hand is at D. At the beginning of each 

 minute the air of the distributing reservoir arriving 

 by the tube j in the distributing box is sent into 

 the main distributing pipes by the tube M. At the 

 end of twenty seconds a displacement of the lever G 

 places the valve R in its second position. The tube 

 A' then communicates with the tube K, open to the 

 atmosphere, while the tube J no longer communicates 

 either with K or with N. The valve R remains 40 seconds 

 m this ])osition, to complete the minute, when a new dis- 

 placement of the valve again places J in connection with 

 N, and so on. All these displacements of the valve are 

 effected by means of gearings arranged in the works 



of the distributing clock. The compressed air of the 

 main pipes is utilised to wind up automatically the two 

 movements by means of the levers A and B, which are 

 connected with pistons placed in the cylinders C, and 



raised every minute by the compressed air to a distance 

 exactly equal to that through which the motor weight has 

 descended during the preceding minute. There is no 

 need, therefore, to trouble about the winding up of the 



