If a number on switchboard A calls for a number on switchboard C, the operator at A connects her subscriber by a jack cord to a trunk line running to C, where the operator similarly connects the trunk line with the number asked for, after ringing up the subscriber. The central exchange of one town is connected with that of another by one or more trunk lines, so that a subscriber may speak through an indefinite number of exchanges. So perfect is the modern telephone that the writer remembers on one occasion hearing the door-bell ring in a house more than a hundred miles away, with which he was at the moment in telephonic connection, though three exchanges were in the circuit.
SUBMARINE TELEPHONY.
Though telegraphic