266.  Over  very  heavy  gradients  the  number  of  engines  on  the  train  is
increased  so  as  to  help  the  train  over,  and  in  one  place  I  saw  four  engines,
two  in  front  and  two  in  rear,  taking  a  train  over  a  12  miles  long  gradient  of
from  1 '  8  to  2  per  cent. ;   and  I  was  told  this  was  the  daily  practice.     At
the  summit  of  the  mountain  there  is  a  tunnel  in  which  the  gradient  changes
from  rising  to  falling.     As  the  train  gets  over  this  hump  the  forward  engine
detaches  while  the  train  is  still   in  motion,  and  runs  ahead  into  a  loop,  the
rear  engines  doing  the  same  thing.     The  points  leading  to  this  loop  are
operated  from  the  signal  tower,  and  are  set  for  the  loop  as  the  train  passes
the  hump,  intimation  of  which  is  automatically  indicated  to  the  signalman.
Similarly,  when  the  crossing  has  been  cleared,  an  indicator  in  the  tower
shows  this,  and  until  it  is  cleared,  the  signal  controlling  the  train  cannot  be
lowered.
89

Trains,  Marshalling  of.
Paras.  267—272.
