The  river  at  this  point  is  about  1200  feet  wide.  It  is
separated  by  Bluff  Island  into  two  channels,  the  westerly  about
400,  the  easterly  some  800  feet  in  width.  The  ordinary
summer  flow  of  the  Hudson  at  this  point  may  be  placed  at
4000  or  5000  cubic  feet  per  second,  though  often  falling  much
below  the  lower  figure.  The  available  fall  is  1 8  feet.  The
westerl}^  channel  is  occupied  b\-  the  power-house,  supplemented
by  a  bulkhead  rising  above  high  water,  and  is  entirely  closed
to  the  passage  of  floods.  The  easterly  channel  is  occupied  by
the  overflow-dam  already  noticed,  page  137.  A  floating
boom,  anchored  to  timber  cribs  filled  with  stone,  extends
obliquely  across  the  westerly  channel  for  the  exclusion  of  drift.
The  lower  part  of  the  povver-house  is  of  concrete  resting  on
rock.  The  floor  is  formed  b\-  arches  springing  from  steel  bo.x
girders  which  are  supported  by  steel  I-beam  columns.  A  con-
crete head-wall  6  feet  thick  divides  the  floor  into  two  parts.
The  up-stream  portion  is  the  flume,  containing  the  wheels  and
draft-tubes.  The  down-.stream  part  is  the  generator-room,
which  the  horizontal  shafts  enter  through  stuffing-boxes  in
plates  built  into  the  concrete  wall.  Along  the  up-stream  face
of  the  power-house  runs  a  rack  formed  of  flat  steel  rods,  sus-
tained by  a  frame  of  steel  beams  and  pillars,  the  whole  sur-
mounted by  a  bridge  for  the  convenience  of  workmen  in
cleaning  the  racks.      There  are  ten   pairs  of  42-inch  horizontal

*  The  drawings    and  description    of  this    plant    are  from    Engineering
News,  vol.  XL.  p.  130,  and  EtigineeringRecord,  vol.  xx.xvni.  p.  299.
5o6


THE   POWER-HOUSE.
MECHANICSVILLE    OX    THE   HUDSON.
