Jtdy 8, 1880] 



NA TURE 



227 



distributincr clock. This clock is regulated by the Ob- 

 servatory, by hand; but soon a special system \vi)l be 

 established, by which the exact time will be distributed 

 from the Observatory by electricity. As the system is 

 established in duplicate at the central works, should any- 

 thino- £jo wrong with one clock the other is put m working 

 ordel- in a few seconds. The function of the distributing 

 clock may be performed by the hand by working properly. 



every minute, the three-way tap, I, which plays exactly 

 the part of the valre R. 



For the system of distribution the air is sent every minutfr 

 into the tube N, which bifurcates into a certain number of 

 smaller branches, forming so many networks completely 

 separate and independent, so that a derangement of one 

 of the systems does not affect the others. The principal 

 tubes, carried underground, are of wrought iron, and have 



Fig. 3. — The Pneumatic Clock 



an internal diameter of 27 millimetres. The tubes placed in 

 private houses are of lead, 15 mm. in diameter; in apart- 

 ments and passages this diameter is reduced to 6 mm., 

 and the tube attached to the clock, in lead or india-rubber 

 coveredwithsilkjis only 3mm. in diameter. Witha pressure 

 of seven-tenths of an atmosphere, by leaving the distri- 

 buting system for 20 seconds in communication with the 

 distribut'ing reservoir, as we have said, it is easy to set 

 the clocks going several miles from the central works, 



notwithstanding the inevitable escape from the pipes. 

 Differences have occasionally been obser\-ed betweea 

 some of the clocks, probably in most cases the results of 

 mischievous meddling; these, and other accidents, how- 

 ever become fewer and fewer, and will no doubt gradually 

 disappear. Owing to the division of the service into 

 various distinct networks, any flaw is soon detected and 



easilv repaired. , 



Whatever be the form or size of the dial, public or 



