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Spherical  Aberration. — A  defect  where-
by a  lens  or  mirror  with  spherical  faces
fails  to  produce  in  its  images  the  correct
outlines  of  objects,  owing  to  the  fact  that
the  curvature  of  one  or  both  of  its  faces
should  slightly  depart  from  the  true
spherical  form  in  order  to  produce  a  true
image.
Spherical  Armature. — An  armature  for
a  dynamo,  the  coils  of  which  are  wound
on  a  spherical  iron  core.
Spherical  Bougie  Decimale. — (1)  A  unit
of  luminous  flux  equal  to  that  which
would  be  produced  by  a  point  source
having  an  intensity  of  one  bougie  deci-
male  in  all  directions.  (2)  A  luminous
flux  equal  to  12.566  lumens.
Spherical  Candle-Power. — (1)  The  total
flux  of  light  emitted  by  a  luminous  source
divided  by  12.566.  (2)  The  candle-power  of
a  point-source,  which  emits  with  uniform
intensity  in  all  directions,  as  much  light
as  does  an  actual  lamp.  (&  The  average
candle-power  of  a  luminous  source  taken
in  all  directions,  or  considered  over  the
entire  surface  of  an  enveloping  sphere.
Spherical  Candle-Power  Measurer. —
An  instrument  for  measuring,  or  ena-
bling to  be  measured,  the  mean  spherical
candle-power  of  a  source  of  light  from  a
single  observation.
Spherical  Candle-Power  Photometer.
(1)  A  photometer  designed  to  measure
the  mean  spherical  candle-power  of  a
lamp.  (2)  A  photometer  designed  to
measure  the  mean  spherical  candle-power
of  a  luminous  source  from  a  single  ob-
servation.
Spherical  Harmonics.  —  Homogeneous
functions  of  rectilinear  space-co-ordinates
which  satisfy  Laplace's  equation.
Spherical  Strain  Insulator. — An  insu-
lator for  a  guy-wire  or  trolley  pull-off,
spherical  in  form.
Spherorneter. — An  apparatus  for  readily
measuring  the  curvature  of  a  sphere.
Sphygmogram. — A  record  made  by  a
sphygmograph.
