IN  the  history  of  human  inventions  and  discoveries,  the  idea
of  the  lightning  conductor  is  almost  the  sole  one  which
sprang,  all  but  perfect,  from  one  brain,  like  Minerva,
in  Greek  mythology,  from  Jupiter's  head.  Benjamin
Franklin  discovered  the  lightning  conductor,  and,  except
some  important  improvements  in  its  manufacture,  due  to
the  progress  of  the  metallurgical  arts,  the  conductor  re-
mains the  same,  in  essence,  as  designed  by  the  world-
famous  citrzen  of  Philadelphia.  The  reason  of  this  is  plain
enough.  Though  one  of  the  most  brilliant  discoveries  in  the
annals  of  mankind,  the  lightning  conductor,  by  itself,  is  one
of  the  simplest  of  things.  Franklin  found  by  experiments,
that  the  mysterious  so-called  '  electric  fluid  '  had  a  tendency
to  make  its  way  in  preference  through  metals,  and  so  he
recommended  the  laying-down  of  a  metallic  line  from  the
clouds  to  the  earth  to  prevent  damage  to  surrounding
objects,  such  as  buildings  and  the  human  beings  within
them.  More  than  this  he  did  not  know  ;  and  more  than  this
we,  to  this  day,  do  not  know.  Of  the  inner  nature,  or  con-
stitution, of  that  grand  cosmic  discharge  of  electricity  to
which  the  name  of  lightning  is  given,  no  scientific  explana-
tion can  be  given.  We  are  utterly  ignorant  of  it,  and  in  all
probability  ever  will  be.
But  while  the  general  principle  laid  down  by  Franklin,
that  metals  will  conduct  the  electric  force  harmlessly  from
the  clouds  to  the  earth,  remains  the  same,  very  much

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50  LIGHTNING   CONDUCTORS.
has  been  learnt,  in  the  progress  of  scientific  investigation,  as
regards  the  varying  conducting  capacity  of  different  metals.
