INTERNATIONAL  TRADE  151

and  when  the  conditions  attending  its  use
are  so  thoroughly  known  to  him  that  he  can,
without  much  trouble  and  delay,  take  the
requisite  steps  to  protect  it  if  prudence  so
dictates.  Of  course,  we  should  be  mistaken
in  saying  that  labour  is  absolutely  immobile
internationally.  Labour  flows  from  any  centre
all  over  the  world,  but  it  flows  with  less  ease
between  places  with  different  languages  than
between  places  with  the  same  language,  with
less  ease  again  between  different  empires  than
between  regions  forming  parts  of  the  same
empire,  and  with  less  ease  yet  again  between
a  country  and  its  colonies  than  between
different  parts  of  the  same  country.  Capital
also  overflows  national  boundaries,  but  only
as  a  rule  under  the  persuasion  of  a  more
than  usually  generous  rate  of  interest  ;  and  in
so  far  as  capital  goes  abroad,  it  will  be  found
that  its  favourite  investments  are  public
securities,  and  such  industrial  stock  as  is
closely  related  to  them.
As  we  have  now  formed  a  general  idea  of
the  problem  of  international  exchange  we
may  at  once  proceed  to  its  detailed  solution.
It  will  be  convenient  to  do  so  by  laying  down
a  series  of  propositions.  The  one  which  is
logically  the  first  is  the  following,  that