﻿102 
  Messrs. 
  R. 
  M. 
  Deeley 
  and 
  P. 
  H. 
  Parr 
  on 
  

  

  near 
  the 
  middle 
  drawn 
  in 
  the 
  direction 
  o£ 
  the 
  stream-lines 
  

   give 
  the 
  following 
  heights 
  above 
  the 
  sea 
  : 
  — 
  

  

  Section 
  IV. 
  Section 
  VI. 
  

  

  2587 
  2640 
  

  

  2592 
  2646 
  

  

  2593 
  2643 
  

   2591 
  2647 
  

  

  4)10363 
  4)10581 
  

  

  2590-8 
  2645 
  

  

  2590-8 
  

  

  54 
  - 
  2 
  metres. 
  

  

  We 
  thus 
  have 
  54*2 
  metres 
  fall 
  in 
  600 
  metres, 
  or 
  a 
  slope 
  of 
  

   9 
  in 
  100. 
  

  

  Weinberg 
  gives 
  the 
  slope 
  as 
  17 
  in 
  1000 
  for 
  this 
  section, 
  a 
  

   much 
  smaller 
  figure. 
  How 
  he 
  obtained 
  it 
  is 
  not 
  stated. 
  

  

  Viscosity 
  of 
  the 
  Glacier 
  Ice. 
  — 
  We 
  have 
  seen 
  that 
  Weinberg 
  

   calculated 
  the 
  viscosity 
  by 
  fitting 
  to 
  the 
  section 
  of 
  the 
  glacier 
  

   a 
  semi-ellipse 
  which 
  he 
  regarded 
  as 
  the 
  equivalent 
  of 
  the 
  

   actual 
  glacier 
  section. 
  We 
  purpose 
  giving 
  a 
  method 
  by 
  

   which 
  the 
  ellipse 
  maybe 
  very 
  accurately 
  fitted 
  to 
  the 
  channel. 
  

   A 
  form 
  of 
  curve 
  will 
  also 
  be 
  described, 
  and 
  used 
  for 
  calcu- 
  

   lating 
  the 
  viscosity, 
  which 
  resembles 
  that 
  of 
  a 
  glaciated 
  

   valley 
  section 
  much 
  more 
  closely 
  than 
  does 
  an 
  ellipse. 
  

  

  The 
  error 
  that 
  may 
  result 
  from 
  the 
  matching 
  of 
  the 
  ellipse 
  

   to 
  the 
  actual 
  section 
  arises 
  from 
  the 
  fact 
  that, 
  although 
  the 
  

   areas 
  may 
  be 
  the 
  same, 
  the 
  deep 
  central 
  channel 
  of 
  the 
  

   Hintereis 
  Glacier 
  has 
  a 
  much 
  greater 
  effect 
  upon 
  the 
  flow 
  

   than 
  a 
  similar 
  cross-section 
  area 
  high 
  on 
  the 
  sides. 
  How- 
  

   ever, 
  the 
  error 
  is 
  only 
  serious 
  when 
  the 
  flux 
  has 
  to 
  be 
  

   calculated. 
  

  

  The 
  method 
  adopted 
  for 
  fitting 
  the 
  ellipse 
  to 
  the 
  actual 
  

   valley-section 
  will 
  now 
  be 
  described. 
  

  

  Fig. 
  11 
  is 
  intended 
  to 
  represent 
  a 
  portion 
  of 
  the 
  side 
  of 
  a 
  

   glacier 
  of 
  considerable 
  width. 
  Here 
  the 
  surface 
  velocity 
  

   is 
  proportional 
  to 
  the 
  square 
  of 
  the 
  depth, 
  or 
  to 
  as 
  2 
  , 
  and 
  we 
  

   may 
  take 
  it 
  that 
  the 
  effect 
  of 
  other 
  portions 
  of 
  the 
  bed 
  on 
  

   each 
  side 
  of 
  the 
  line 
  AB 
  has 
  no 
  influence 
  on 
  the 
  velocity 
  

   at 
  A, 
  when 
  the 
  glacier 
  bed 
  is 
  flat. 
  When 
  the 
  lower 
  surface 
  

   is 
  not 
  flat 
  the 
  velocity 
  at 
  C 
  is 
  considerably 
  influenced, 
  and 
  it 
  

   is 
  desirable 
  to 
  ascertain, 
  as 
  near 
  as 
  possible, 
  what 
  this 
  in- 
  

   fluence 
  is. 
  When 
  the 
  channel 
  is 
  elliptical 
  

  

  *^2T^+Pj 
  (12) 
  

  

  