Page:Popular Science Monthly Volume 20.djvu/322

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308
THE POPULAR SCIENCE MONTHLY.
PSM V20 D322 Map of paris with observatory circuit outlined in black.jpg
Fig. 3.—Map of Paris. The two circuits from the Observatory are represented by heavy black lines;

the Seine; the regulator at the Hotel de Ville automatically sends a current into twenty relays at precisely one hundred seconds before the end of each hour, and thus cuts these wires off from their ordinary telegraphic duty and places them in the circuits of the different mairies. Then, at twelve seconds before the end of the hour, the regulator sends another current into the circuit of the mairies; this current is stopped precisely at the end of the hour. At each mairie the clock automatically shuts off the wire from the telegraph and connects it