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.