It  must  be  added,  however,-  that  when  the  rudder  is  in  use  the
screw  also  exercises  a  steering  effect  of  the  kind  described,  dud
makes  it  possible  .to  turn  a  ship  more  quickly  in  one  direction
than  in  another,  when  she  is  moving  ahead.  The  difference  in
the  times  of  turning  is  more  considerable  in  some  cases  than  in
others.  For  example,  in  the  BelleropJum  turning  to  starboard  the
circle  was  completed  in  4  minutes ;  but  turning  to  port,  a  circle
of  the  same  diameter  occupied  4  minutes  20  seconds.  In  the
floating  battery  Terror,  where  the  peculiar  shape  of  the  stem
gave  a  great  excess  of  thrust  to  the  upper  blades,  the  circle  with
starboard  helm  occupied  5  minutes    12  seconds,  and  that  with


♦  See  also  Professor  Osborne  Reynolds'  Paper  in  the  ^Transactions  of  the
Institution  of  Naval  Architects  for  1873.
