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POLITICAL  ECONOMY

effected  by  the  process  of  barter,  which  is
apt  not  only  to  try  the  patience,  but  also  to
fail  to  effect  satisfactorily  the  purposes  of
exchange.  Its  successful  completion  implies
in  every  case  a  perfect  double  coincidence  of
wants.  In  order  to  do  business  by  barter,  it  is
necessary  that  a  person  should  find  some
other  person  who  not  only  possesses  what  the
first  wants,  but  also  wants  what  the  first  has
to  offer.  And  it  implies  many  other  conditions
which  are  notable  by  their  absence  commonly.
The  exchange  of  cattle  on  equitable  terms  for
a  limited  quantity  of  small  things  would  be
found  difficult,  since  a  living  ox  is  indivisible.
Moreover,  when  there  is  no  common  medium  of
exchange,  it  is  not  easy  to  find  out  what  the
exchange  value  of  things  should  be  in  view  of
the  state  of  demand  and  supply.  To  know
the  value  of  wheat  involves  knowing  how
competition  has  settled  its  exchange  rate
against  iron  and  clothing  and  other  forms
of  food  and  furniture  and  what  not.  With
the  object—though  not  perhaps  with  the
deliberate  design—of  escaping  the  multitude
of  inconveniences  associated  with  barter,
people  got  into  the  habit  of  selecting  one  or
a  few  things  to  receive  in  payment  for  what
they  sold  and  to  make  purchases  with.  The
thing  or  things  chosen  were  naturally  articles