But  still  I  do  not  know  how  to  get  the
cold  water  into  the  body  of  the  pump,  I
mean  into  the  cylinder,  to  condense  the
steam."

"  The  steam,"  said  Harry,  "  is  let  off
into  a  separate  vessel,  called,  from  its  use,
a  condenser.  This  vessel  is  surrounded  by
cold  water,  so  that  the  steam  is  condensed,
as  soon  as  it  comes  into  it."

"And  is  this  all  the  steam  engine?"
said  Lucy.
"  No,  my  dear  Lucy,  it  is  only  the
general  principle.  I  cannot  explain  all
to  you,  I  should  only  puzzle  you.  There
are  different  sorts  of  steam  enoines.  In

O

that  invented  by  Mr.  Watt,  the  expansive
force  of  the  steam  is  used  in  different
degrees,  to  raise  the  piston,  and  to  force
it  down."


168

"  I  did  not  know  that  the  steam  was
ever  let  in  above  the  piston,"  said  Lucy.
"  Yes,  it  is.  I  did  not  tell  you  that  at
first,  lest  I  should  puzzle  you,  and  I  will
not  now  tell  you  exactly  how  it  is  done.
And  there  is  a  great  deal  more  to  be  ex-
plained, about  the  ways  of  making  the
steam  engine  raise  weights,  or  water,  or
work  machinery,  in  different  directions.
