﻿the 
  Viscosity 
  of 
  Glacier 
  Ice. 
  97 
  

  

  that 
  in 
  the 
  case 
  o£ 
  the 
  Glacier 
  des 
  Bois 
  the 
  locus 
  of: 
  maximum 
  

   velocity 
  was 
  on 
  the 
  outside 
  of 
  the 
  centre 
  line 
  of 
  the 
  curve. 
  

  

  Perhaps 
  the 
  most 
  satisfactory 
  method 
  of 
  procedure 
  for 
  

   ascertaining 
  the 
  probable 
  slip 
  from 
  these 
  curves, 
  is 
  to 
  compare 
  

   Weinberg's 
  pitch 
  curve 
  with 
  the 
  actual 
  curve 
  after 
  making 
  

   them 
  symmetrical 
  mean 
  curves. 
  These 
  are 
  given 
  in 
  fig. 
  6. 
  

   With 
  no 
  slip 
  in 
  the 
  case 
  of 
  the 
  pitch 
  curve, 
  the 
  curves 
  do 
  not 
  

   match 
  at 
  all 
  well. 
  With 
  74 
  per 
  cent, 
  slip 
  a 
  more 
  satisfactory 
  

   agreement 
  is 
  obtained, 
  a' 
  a! 
  is 
  the 
  pitch 
  curve 
  obtained 
  by 
  

   Weinberg, 
  no 
  slip 
  being 
  allowed, 
  and 
  aa 
  is 
  the 
  same 
  curve 
  

   with 
  an 
  allowance 
  of 
  74 
  per 
  cent. 
  slip. 
  Using 
  this 
  curve 
  as 
  

   a 
  guide 
  for 
  the 
  extrapolation 
  of 
  the 
  actual 
  mean 
  curve 
  bb, 
  

   we 
  get 
  a 
  slip 
  of 
  68*7 
  per 
  cent. 
  

  

  Considering 
  that 
  the 
  broken 
  ice 
  at 
  the 
  sides 
  must 
  have 
  

   resulted 
  to 
  some 
  extent 
  in 
  the 
  shoulders 
  A, 
  fig. 
  6, 
  being 
  relieved 
  

   of 
  resistance, 
  that 
  the 
  upper 
  portion 
  of 
  the 
  ice 
  is 
  " 
  wet" 
  and 
  

   has 
  a 
  low 
  viscosity, 
  and 
  that 
  the 
  slip 
  at 
  the 
  sides 
  may 
  be 
  less 
  

   than 
  at 
  the 
  middle, 
  68*7 
  per 
  cent, 
  of 
  slip 
  is 
  probably 
  much 
  

   too 
  great. 
  

  

  The 
  resistance 
  offered 
  to 
  the 
  flow 
  of 
  a 
  glacier 
  is 
  of 
  two 
  

   kinds 
  (1) 
  the 
  frictional 
  resistance 
  of 
  the 
  floor, 
  and 
  (2) 
  the 
  

   resistance 
  the 
  ice 
  offers 
  to 
  change 
  of 
  shape. 
  When 
  the 
  form 
  

   of 
  the 
  floor 
  is 
  regular 
  and 
  smooth 
  the 
  glacier 
  may 
  slide 
  

   bodily 
  down 
  the 
  valley. 
  Prof. 
  Tarr 
  * 
  thus 
  refers 
  to 
  Fallen 
  

   Glacier, 
  Alaska. 
  " 
  This 
  glacier 
  .... 
  lay 
  for 
  the 
  most 
  part 
  

   in 
  a 
  cirque-like 
  amphitheatre 
  with 
  steeply 
  rising 
  mountain 
  

   ^alls 
  at 
  its 
  head." 
  "The 
  glacier 
  was 
  photographed 
  by 
  

   Russell 
  in 
  1890/' 
  " 
  The 
  amphitheatre 
  has 
  a 
  narrow 
  mouth, 
  

   out 
  of 
  which 
  the 
  crevassed 
  terminus 
  of 
  the 
  glacier 
  pro- 
  

   truded, 
  the 
  lower 
  end 
  terminating 
  at 
  an 
  elevation 
  of 
  about 
  

   1000 
  feet 
  above 
  the 
  fiord." 
  It 
  was 
  estimated 
  to 
  have 
  a 
  

   length 
  of 
  about 
  a 
  mile. 
  Some 
  Indian 
  guides 
  reported 
  the 
  

   fall 
  of 
  the 
  glacier, 
  and 
  Tarr 
  found 
  that 
  " 
  the 
  entire 
  glacier 
  

   had 
  evidently 
  shot 
  out 
  of 
  its 
  valley, 
  tumbled 
  a 
  thousand 
  feet 
  

   down 
  the 
  steep 
  slope, 
  and 
  entered 
  the 
  fiord, 
  generating 
  a 
  

   series 
  of 
  pronounced 
  waves." 
  " 
  A 
  half 
  mile 
  south 
  of 
  Fallen 
  

   Glacier 
  the 
  wave 
  rose 
  110 
  feet, 
  breaking 
  off 
  alder 
  bushes 
  at 
  

   that 
  height." 
  No 
  doubt 
  the 
  fall 
  was 
  greatly 
  assisted 
  by 
  the 
  

   crevassing 
  of 
  the 
  ice. 
  

  

  The 
  coefficient 
  of 
  friction 
  of 
  a 
  glacier 
  on 
  its 
  bed 
  depends 
  

   largely 
  upon 
  the 
  presence 
  of 
  rock 
  material 
  embedded 
  in 
  its 
  

   under 
  surface. 
  Indeed 
  the 
  slip 
  and 
  friction 
  of 
  glaciers 
  must 
  

   vary 
  greatly 
  with 
  the 
  nature 
  of 
  the 
  rocks 
  over 
  which 
  they 
  

   flow. 
  

  

  * 
  'The 
  Yakutat 
  Bay 
  Region 
  of 
  Alaska,' 
  1909, 
  p. 
  67. 
  

   Phil. 
  May. 
  S. 
  6. 
  Vol. 
  26. 
  No. 
  151. 
  July 
  1913. 
  H 
  

  

  