WAGES,  PROFITS  AND  INTEREST  175

provisionally  assume  that  all  the  land  is  equally
valuable  in  respect  of  fertility  and  situation.
If  the  population  is  so  dense  that  the  whole
of  the  land  is  in  use,  the  land  will  have  a
marginal  worth  per  acre  equal  to  the  difference
that  would  be  made  to  the  product  by  the
removal  of  one  acre.  If,  however,  the  population ­
  is  such  that  the  whole  of  the  land  is  not
occupied,  land  will  have  no  marginal  worth,
because,  like  air,  there  is  more  than  enough
of  it.  It  is  premised,  of  course,  that  the
land  is  not  monopolised.  When  land  is  not
monopolised,  its  value  is  governed  by  the
marginal  worth  of  different  quantities  of  land
in  relation  to  what  the  fixed  supply  is.
The  supply  of  labour  will  engage  our  attention ­
  next.  Here  we  discover  more  complex
conditions.  The  size  of  the  population  is
certainly  dependent  in  some  degree  upon
earnings—other  things  being  equal  it  may  not
infrequently  happen  that  population  rises
as  earnings  rise—but  the  laws  of  population
are  so  obscure  that  all  sweeping  and  dogmatic
pronouncements  must  be  viewed  with
suspicion.  What  is  perfectly  certain,  however,
is  that  the  relative  wages  paid  in  many  or
most  trades  settle  the  supply  of  labour
offered  in  those  trades.  Were  the  wages
of  carpenters  to  rise,  other  wages  remaining