In the above figure, 23, let the right hand side represent Washington, and the left, Baltimore. The lines marked 1, 2, 3, 4, 5, and 6, between _m_ and _k_, respectively, represent the six wires connecting (for example) Washington with Baltimore. Each cluster of black dots, P and N, represent the batteries of that line upon which it is placed. There are three batteries at W, and three at B; _m_ 1, _m_ 3, and _m_ 5, represent the three magnets, or registers, and _k_ 2, _k_ 4, and _k_ 6, the three keys, or correspondents, at Baltimore; _k_ 1, _k_ 3, and _k_ 5, are the three keys, or correspondents, and _m_ 2, _m_ 4, and _m_ 6, the three magnets, or registers, at Washington. C B is the copper plate at Baltimore, and C W, the copper plate at Washington, one at each terminus. In order to operate the six lines, simultaneously, if required by the pressure of telegraphic communications, there must be three operators at each station, commanding their respective keys, and presiding at their respective registers. If the three operators at Washington choose to write in Baltimore, together, or in succession, on their respective registers at the latter place, the galvanic current of the three lines 1, 3, and 5, takes this direction. Commencing at the point, P, of the three batteries, 1, 3, and 5, at W, it passes to _k_, of the keys; thence along the wires to _m_, the magnets, 1, 3, and 5 at B; thence to the single wire, where the three currents join in one to C B, the copper plate; then through the ground to C W, the other copper plate; then up the single line to their respective batteries at the point, N, having each finished its circuit independently of each other. If, in reply, the three operators at Baltimore wish to write upon their registers at Washington, either together, or in any succession, they may choose; the fluid leaves the point, P, of their respective batteries, at Baltimore, 2, 4, and 6; unite in the single wire to C B, the copper plate; then pass through the ground in the direction of arrows to C W, copper plate at Washington, then along the single wire to their respective magnets, _m_, 2, 4, and 6; then along the extended wires to _k_, 2, 4, and 6 at Baltimore; and then to N pole of their respective batteries. In this manner six distinct circuits may be operated independently of each other, at the same time, or in any succession, with only one wire for each, and the ground in common, as a part of the circuit. It is obvious from the above arrangement that if one wire only, extended between two distant points, will suffice to enable communications to be exchanged with each other; that any number of wires extended, will also, each, individually, give a distinct and separate line for telegraphic purposes, independently of all the other lines on the same route. [Illustration: FIG. 24]