se a set of lines of two physical wires each, is not
complicated, though it must be done with care and in accordance with a
definite, foreknown plan. Transposing phantom circuits is less simple,
however, as four wires per circuit have to be transposed, instead of
two.

[Illustration: Fig. 464. Transposition of Phantom Circuits]

In Fig. 464, the general spacing of transposition sections is the usual
one, 1,300 feet, of the _ABCB_ system widely in use. The pole circuit,
on pins _5_ and _6_ of the upper arm, is transposed once each two miles.
The pole circuit of the second arm transposes either once or twice a
mile. But neither pole circuit differs in transposition from any other
regular scheme except in the frequency of transposition. All the other
wires of each arm, however, are so arranged that each wire on either
side of the pole circuit moves from pin to pin at section-ends, till it
has completed a cycle of changes over all four of the pins on its side.
In doing so, each phantom circuit is transposed with proper regard to
each of the other three on that twenty-wire line.

The "new transposition" lettering in Fig. 464 is for the purpose of
identifying the exact scheme of wiring each transposition pole. The
complication of wiring at each transposition pole is increased by the
adoption of phantom circuits. Maintenance of all the circuits is made
more costly and less easy unless the work at points of transposition is
done with care and skill. Phantom circuits, to be always successful,
require that the physical circuits be balanced and kept so.

_Transmission over Phantom Circuits._ Under proper conditions phantom
circuits are better than physical circuits, and in this respect it may
be noted that some long-distance operating companies instruct their
operators always to give preference to phantom circuits, because of the
better transmission over them. The use of phantom circuits is confined
almost wholly to open-wire circuits; and while the capacity of the
phantom circuit is somewhat greater than that of the physical circuit,
its resistance is considerably smaller. In the actual wire the phantom
loop is only half the resistance of either of the physical lines from
which it is made, for it contains twice as much copper. The resistance
of the repeating coils, however, is to be added.

=Simplex.= Simplex telegraph circuits are made from metallic circuit
telephone lines, as shown in Fig. 465. The principle is identical wi