These  two  relays  R  and  R8,  are  placed  in  the
bridge  wire  of  a  \Vheatstone  bridge.  Ti.e  entire
apparatus  of  transmitting  keys  and  relays  is
duplicated  at  each  end  of  the  line.  Under  these
conditions,  signals  transmitted  from  either  end  of
the  line  affect  the  instruments  at  the  other  end  of
the  line,  but  not  th«.ir  own  instruments,  in  the
sime  manner  as  in  the  case  of  the  bridge  du
plex.  (See  Telegraphy,  Duplex,  Bridge  Method
of.}

Telegraphy,    Quadruplex,     Differential


Tel.]


513


[Tel,


Method  of A   system  of  quadruplex

telegraphy  by  means  of  a  double  differential
duplex  system.
Quadruplex  telegraphy  depends  for  its  opera-
tio.i  on  the  use  of  two  differentially  wound  relays
it  each  sta'ion.  One  of  these  relays  A,  as  shown
in  Fi^.  534,  which  shows  the  general  arrangement
of  the  system,  gives  signals  on  a  change  in  the
i.irection  <  I  the  current,  but  none  on  a  change  in
the  current  strength.  The  other  B,  gives  signals
on  changes  in  current  strength,  but  none  on
changes  in  direction.  They  are,  therefore,  in-
dependent of  each  other,  and  operate  sounders
that  are  under  the  independent  control  of  two
distinct  receiving  operators.
A  table,  divided  into  four  sections,  is  provided
with  places  for  two  sending  and  two  receiving
clerks.  The  name  "  A  side  "  is  given  to  the  side
worked  by  the  reversed  currents,  and  the  "B_
side  "to  that  worked  by  the  strengthened  cur-
nnts.
CORRECTING


BATTERY    1.    BATTERY    2.
Fig.  3 3 4.    Quadruple*  Telegraphy,  Differential  Method.
Referring  to  Fig.  534  the  reversing  key  on  the
"  A  side  "  is  merely  indicated  so  as  to  avoid  con-
fusion by  too  great  detail  ;  as  is  also  the  case  with
the  increment  key  or  the  strengthening  key  at  B.
