Surface  Density. — The  quantity  of  elec-
tricity-per-unit-of-area  at  any  point  on  a
charged  surface.
Surface-Efficiency  of  Filament.— (1)
The  efficacy  of  a  particular  character  of
surface  for  luminous  radiation.  (2)  The


luminous  efficiency  of  a  particular  charac-
ter of  surface  in  a  filament.
Surface  Integral.— (1)  The  sum  of  all
the  products  of  a  point  function  and  its
associated  element  of  area,  lying  on  a
surface,  when  the  elements  are  all  in-
definitely small.  (2)  The  integral  of  a
quantity  taken  over  a  surface.
Surface  Integral  of  Magnetic  Induc-
tion.— The  total  magnetic  flux  passing
through  a  surface.
Surface  Magnetization. — In  the  distri-
bution of  imaginary  magnetic  matter,
the  magnetism  residing  on  a  surface,  or
the  so-called  free  magnetism.
Surface-Wound  Armature. — (1)  An  ar-
mature wound  on  its  surface,  as  distin-
guished from  an  iron-clad  armature.  (2)
An  armature  in  which  the  conductors  lie
over  the  surface  of  the  core,  instead  of
being  placed  in  grooves  or  slots  formed
therein.
Surfusion. — A  word  sometimes  employed
for  super-saturation.
Surgical  Lamp. — A  lamp  employed  in
surgical  exploration,  examination,  or  oper-
ation.
Surging  Circuit. — Any  circuit  through
which  a  surging  discharge  is  passing.
Surging  Discharge. — (1)  A  discharge  ac-
companied by  electric  surgings.  (2)  An
oscillatory  discharge.
Surgings,  Electric. — (1)  Electric  oscilla-
tions set  up  in  a  conductor  that  is  under-
going rapid  discharging,  or  in  neighbor-
ing conductors  that  are  being  rapidly
charged  and  discharged.  (2)  Electric
oscillations,  direct  or  induced.
Susceptance. — In  an  alternating-current
circuit,  branch,  or  conductor,  the  quan-
tity whose  square  added  to  the  square  of
the  conductance  is  equal  to  the  square  of
the  admittance.
Susceptibility. — A  word  sometimes  used
for  magnetic  susceptibility.
