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THE POPULAR SCIENCE MONTHLY.
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
