We now proceed to describe the manner of operating with the two instruments, at their respective stations: and, first, we must here designate each needle by its own peculiar mark of reference. Let the two needles upon the wire, A′, be denoted by, A, S and A, T; those of the wire, B′, by B, S and B, T; and those of the wire, C′, by C, S and C, T. It will appear obvious, from the foregoing description, that but _one_ needle of each _wire_, A′, B′, C′, can be made to close its circuit at the same instant. However, _two_ needles, or _three_ needles of _different wires_, may close their circuits at the same instant, but no higher number than three. The various combinations of _one_ mark, _two_ marks, and _three_ marks, upon the same row of six cross divisions of the fabric, constitute the characters representing letters. [Illustration: FIG. 74. LONDON.—_Transmitting Station._] Figure 74 represents the _transmitting_ station, which may be supposed to be _London_, and figure 75, the _receiving_ station, which may be at _Birmingham_, with four wires extending from station to station, or three only, if the _ground_ be substituted for the wire, D, D″. The wires, D, A, B and C, are supposed to be united with D″, A′, B′ and C′, respectively. Now, if we depress the keys, in the following order, we shall, for each key, have the following deflections of the two needles, belonging to each key. No. 1. The keys, H, 7, moves the arm, A, S, to the right, A, T, to the left. “ J, 7, “ A, S, “ left, A, T, “ right. “ K, 7, “ B, S, “ right, B, T, “ left. “ M, 7, “ B, S, “ left, B, T, “ right. “ O, 7, “ C, S, “ right, C, T, “ left. “ U, 7, “ C, S, “ left, C, T, “ right. These are all the various deflections which it is possible to give the six needles. Those, however, which deflect to the right, not closing the circuit, produce no effect, and are of no account. We will, therefore, omit them, and simply give the table, thus: No. 2. The keys, H, 7, move the arm A, T, to the left. No. 1. “ J, 7, “ A, S, “ “ 2. “ K, 7, “ B, T, “ “ 3. “ M, 7, “ B, S, “ “ 4. “ O, 7, “ C, T, “ “ 5. “ U, 7, “ C, S, “ “ 6. [Illustration: FIG. 75. BIRMINGHAM.—_Receiving Station._]