The  volumetric  measurement  of  water  has  been
brought  to  the  greatest  perfection  in  Italy,  where
the  inequalities  in  the  quantity  of  water  furnished
irrigators  led  to  a  struggle  lasting  over  200  years,
culminating  in  the  adoption  of  the  module  of
SoldatL  (Figs.  588  and  589.)

In  this  an  effort  is  made,  by  means  of  the  head-
gate  at  the  upper  end  of  the  box,  to  regulate  the
pressure  on  the  top  of  the  orifice,  and  when  visited
with  sufficient  frequency  by  the  ditch-tenders  the
results  are  approximately  correct.
The  American  counterpart  of  the  Italian  oncia,
the  unit  of  the  Italian  module,  is  the  inch,  which  is
used  in  measuring  water  for  both  irrigation  and
mining.  It  is  the  volume  of  water  which  will  flow
through  an  inch  square  orifice,  under  a  prescribed
pressure  that  varies  from  4  to  8  inches  above  the
top  of  the  orifice.  In  the  United  States  the  larger


and  know  whether  or  not  they  are  getting  the
volume  paid  for.  It  is,  however,  limited  to  the
measurement  of  small  quantities  of  water  and  is
never  of  more  than  approximate  accuracy.  The
weir,  used  in  connection  with  a  clockwork  or
electrical  register  which  keeps  a  constant  record


1

Pis.  591.    BnuUnc  in  alfalfa  seed  before  inigatiiic.
orifices  are  6  inches  in  height  and  of  sufficient
width  to  give  the  required  number  of  inches.
