Resonator,  Electric An  apparatus

employed  by  Hertz  in  his  investigations  on
electric  resonance.  (See  Resonance,  Elec-
tric^

An  «J£rfric  resonator  consists  essentially  of  an


open-circuited  conductor,  or  circuit  of  such  dimen-
sions that  electro-magnetic  waves  or  pulses  are
propagated  through  it  at  the  same  rate  as  those
which  are  occurring  in  a  neighboring  circuit
from  which  electro-magnetic  radiation  is  tak-
ing place.  Under  these  circumstances  electro-
magnetic  pulses  are  set  up  sympathet  cally  by
resonance  in  the  open  circuit  of  the  resonator,  like
the  sympathetic  vibrations  in  a  tuning  fork,  when
placed  near  another  vibrating  tuning  fork,  which
is  giving  off  sound  waves  of  exactly  the  same
period  of  vibration  as  its  own.
Resonator,  Electro-Magnetic A

term  applied  to  the  Hertz  spark  micrometer,
in  which  electro-magnetic  waves  are  produced
by  electric  resonance.  (See  Resonance,  Elec-
tric.)

Resultant. — In  mechanics,  a  single  force
that  represents  in  direction  and  intensity  the
effects  of  two  or  more  separate  forces.
The  separate  forces  are  called  the  components.
(See  Components.)

Retardation.— A  decrease  in  the  speed  of
telegraphic  signaling  caused  either  by  the
induction  of  the  line  conductor  on  itself,  or
by  mutual  induction  between  it  and  neighbor-
ing conductors,  or  by  condenser  action,  or  by
all.
The  line  must  receive  a  certain  charge  before
a  current  sent  into  it  at  one  end  can  produce  a
signal  at  the  other  end.  This  charge  will  de-
pend on  the  length  and  surface  of  the  wire,  on  the
neighborhood  of  the  wire  to  the  earth  or  other
wires,  and  on  the  nature  of  the  insulating  mate
rial  between  the  wire  and  neighboring  conductors.
