Balance,  Hekto-AmpSre An  am-
meter in  the  form  of  a  balance,  whose  scale
is  graduated  to  give  direct  readings  in  hekto-
amperes.  (See  Balance,  Centi- Ampere.}

Balance  Indicator. — (See  Indicator,  Bal-
ance.}

Balance,     Induction,     Hughes'  —

An  apparatus  for  the  detection  of  the  presence
of  a  metallic  or  conducting  substance  by  the
aid  of  induced  electric  currents.
Hughes'  induction  balance  is  shown  in  Fig.  35.
A,  B,  C  and  D  are  bobbins,  wound  with  about
300  feet  of  No.  32  copper  wire.  The  coils  ar«


connected  as  shown,  A  and  B,  in  the  circuit  of  a
battery,  and  C  and  D,  in  the  circuit  of  a  telephone.
The  coils,  A  and  B,  and  C  and  D,  are  placed  at


Fig  33.     Hughes'  Induction  Balance.
such  a  distance  apart  as  to  prevent  any  mutual
induction  occurring  between  them.  The  coils
are  so  joined  that  the  direction  of  the  induction
of  A,  on  C,  is  opposite  to  that  of  B,  on  D.
The  coils,  A  and  B,  then  act  as  primaries,  and  C
and  D,  as  secondaries.  In  the  battery  circuit  is  an
interrupter  I,  which  is  caused  to  continually  make
and  break  the  circuit.
The  coils  are  so  adjusted  that  the  opposing
secondary  coils  produce  but  little  noise  to  one
listening  at  the  telephone.  This  can  readily  be
done  by  the  adjusting  of  a  single  pair  of  coils.
