Head  Guy. — A  guy  attached  to  the  top  of
a  pole.
Head  Guying. — A  method  of  pole  guying
for  checking  lateral  vibrations,  in  which
the  top  of  each  pole  is  guyed  to  the
bottom  of  the  next  succeeding  pole  for
a  distance  of  several  poles.
Head-Lamp. — An  electric  lamp  placed
in  the  focus  of  a  reflector  supported  on
the  head.
Head-Light,  Electric. — An  electric  light
placed  in  the  focus  of  a  parabolic  reflector
in  front  of  an  engine  or  car.
Head  of  Liquid. — (1)  The  vertical  distance
from  the  level  of  a  liquid  in  a  containing
vessel  to  the  centre  of  gravity  of  an  orifice
placed  therein.  (2)  Difference  of  liquid
elevation  or  level.
Head  Receiver. — A  head-gear  telephone-
receiver.
Hearing  Tubes. — Tubes  connecting  a
telephone  receiver  with  the  ears  of  the
listener.
Heat.— (1)  A  form  of  energy.  (2)  A  mode  of
motion.  (3)  A  vibratory  motion  impressed
on  the  molecules  of  matter  by  the  action
of  any  form  of  energy.  (4)  A  wave  mo-
tion impressed  on  the  universal  ether  by
the  action  of  some  form  of  energy.
Heat  Alarm. — A  temperature  alarm.
Heat  Coil. — (1)  A  form  of  protector  for
switchboards  or  receptive  apparatus  gen-
erally, consisting  of  a  coil  of  fine  German
silver  wire  wrapped  around  a  small  me-
tallic plug,  held  in  its  place  by  a  drop  of
readily  fusible  solder,  and  so  arranged
that  on  the  melting  of  the  solder  a  spring
is  permitted  to  act  so  as  to  dead-ground
the  system.  (2)  A  form  of  sneak-current
arrester.
Heat,  Electric.— The  heat  developed  by
the  passage  of  an  electric  current  through
a  conductor.
Heat  Insulator. — Any  non-conductor  of
heat.
