﻿96 
  Messrs. 
  R. 
  M. 
  Deeley 
  and 
  P. 
  H. 
  Parr 
  on 
  

  

  the 
  ice 
  is 
  very 
  much 
  crevassed 
  and 
  lags 
  behind 
  on 
  that 
  

   account. 
  

  

  Another 
  method 
  of 
  estimating 
  the 
  slip 
  is 
  to 
  find 
  the 
  

   amount 
  o£ 
  slip 
  which 
  brings 
  the 
  actual 
  surface 
  velocity 
  curve 
  

   into 
  agreement 
  with 
  the 
  theoretical 
  one. 
  

  

  In 
  the 
  absence 
  of 
  a 
  knowledge 
  of 
  the 
  viscosity 
  or! 
  the 
  

   liquid 
  it 
  would 
  be 
  impossible 
  to 
  calculate 
  the 
  actual 
  velocity 
  

   curve 
  ; 
  but 
  although 
  this 
  cannot 
  be 
  done, 
  the 
  form 
  of 
  the 
  

   velocity 
  curve 
  for 
  certain 
  shaped 
  sections 
  can 
  be 
  obtained 
  

   with 
  accuracy. 
  In 
  the 
  case 
  of 
  an 
  irregular 
  section, 
  however, 
  

   such 
  as 
  that 
  of 
  the 
  Hintereis 
  Glacier, 
  this 
  can 
  only 
  be 
  done 
  

   approximately. 
  

  

  Unfortunately 
  the 
  semicircle 
  or 
  semiellipse 
  is 
  of 
  no 
  use 
  

   for 
  this 
  purpose 
  ; 
  for 
  the 
  form 
  of 
  the 
  glacier 
  section 
  differs 
  

   markedly 
  from 
  that 
  of 
  an 
  ellipse. 
  Generally 
  speaking, 
  the 
  

   sectional 
  form 
  of 
  a 
  glaciated 
  valley 
  approaches 
  the 
  parabolic 
  

   form 
  very 
  closely 
  ; 
  but 
  the 
  deepest 
  part 
  is 
  frequently 
  not 
  at 
  

   the 
  centre. 
  

  

  From 
  equations 
  (4) 
  (5) 
  and 
  (6) 
  we 
  see 
  that 
  for 
  an 
  ellipse 
  

  

  Vb 
  2 
  

  

  for 
  the 
  central 
  velocity, 
  

  

  where 
  ^='hirv 
  ( 
  9 
  ) 
  

  

  p 
  +1 
  

  

  and 
  p 
  = 
  ratio 
  of 
  semi-width 
  to 
  depth. 
  

  

  If 
  it 
  were 
  possible 
  to 
  find 
  such 
  values 
  for 
  F 
  that 
  the 
  

   equation 
  could 
  be 
  used 
  at 
  any 
  part 
  of 
  an 
  irregular 
  section, 
  it 
  

   would 
  be 
  possible 
  to 
  calculate 
  the 
  form 
  of 
  the 
  speed 
  curve 
  

   for 
  that 
  section. 
  Such 
  a 
  method 
  would 
  be 
  probably 
  a 
  purely 
  

   empirical 
  one 
  ; 
  but 
  if 
  the 
  results 
  obtained 
  for 
  a 
  section, 
  the 
  

   actual 
  form 
  of 
  the 
  speed 
  curve 
  of 
  which 
  is 
  known, 
  proved 
  

   approximately 
  correct, 
  the 
  method 
  could 
  then 
  be 
  used 
  with 
  

   some 
  confidence 
  for 
  the 
  irregular 
  glacier 
  section. 
  

  

  Weinberg 
  experimented 
  with 
  pitch 
  flowing 
  down 
  a 
  channel 
  

   of 
  the 
  same 
  section 
  as 
  that 
  given 
  by 
  Bliimcke 
  and 
  Hess 
  for 
  

   the 
  Hintereis 
  Glacier. 
  His 
  curve 
  aa 
  is 
  shown 
  in 
  fig. 
  5, 
  upper 
  

   section, 
  along 
  with 
  the 
  actual 
  glacier 
  velocity 
  curve 
  bb. 
  The 
  

   most 
  striking 
  difference 
  is 
  the 
  fact 
  that 
  the 
  maximum 
  speed 
  

   of 
  the 
  Hintereis 
  Glacier 
  is 
  to 
  the 
  right 
  (north) 
  of 
  the 
  centre 
  

   line, 
  whereas 
  the 
  maximum 
  speed 
  of 
  the 
  pitch 
  velocity 
  curve 
  

   is 
  nearly 
  above 
  the 
  deepest 
  part 
  to 
  the 
  south. 
  This 
  may 
  in 
  

   great 
  measure 
  be 
  due 
  to 
  the 
  slight 
  curve 
  of 
  the 
  glacier 
  and 
  

   the 
  direction 
  in 
  which 
  the 
  ice 
  current 
  flows 
  from 
  the 
  neve 
  

   region. 
  The 
  map 
  fig. 
  3 
  will 
  explain 
  this. 
  Tyndall 
  showed 
  

  

  