﻿the 
  Viscosity 
  of 
  Glacier 
  Ice. 
  99 
  

  

  at 
  the 
  middle. 
  Accepting 
  68*7 
  per 
  cent, 
  as 
  being 
  the 
  slip 
  

   at 
  the 
  sides, 
  an 
  allowance 
  of 
  24 
  per 
  cent, 
  for 
  the 
  slip 
  at 
  the 
  

   middle 
  gives 
  us 
  52*2 
  per 
  cent, 
  as 
  the 
  probable 
  slip 
  at 
  the 
  

   middle. 
  

  

  Formula 
  (11) 
  does 
  not 
  give 
  accurate 
  results, 
  because 
  it 
  

   assumes 
  that 
  the 
  slip 
  at 
  one 
  point 
  may 
  be 
  different 
  from 
  that 
  

   at 
  another 
  point 
  near 
  by 
  without 
  there 
  being 
  any 
  mutual 
  

   effect. 
  However, 
  the 
  figures, 
  except 
  near 
  the 
  sides, 
  show 
  

   that 
  the 
  slip-difference 
  is 
  small, 
  and 
  will 
  not 
  seriously 
  affect 
  

   the 
  figures. 
  

  

  It 
  must 
  be 
  admitted 
  that 
  the 
  results 
  obtained 
  by 
  a 
  con- 
  

   sideration 
  of 
  the 
  surface 
  velocity 
  curve 
  do 
  not 
  give 
  results 
  

   which 
  can 
  be 
  considered 
  very 
  satisfactory 
  ; 
  but 
  this 
  has 
  

   been 
  relied 
  upon 
  by 
  Weinberg 
  for 
  estimating 
  the 
  slip. 
  He, 
  

   however, 
  took 
  the 
  averages 
  of 
  many 
  sections, 
  instead 
  of 
  

   confining 
  himself, 
  as 
  we 
  have 
  done, 
  to 
  section 
  V. 
  of 
  Blumcke 
  

   and 
  Hess, 
  and 
  estimated 
  the 
  slip 
  at 
  about 
  33 
  per 
  cent. 
  

  

  Another 
  method 
  of 
  calculating 
  the 
  slip 
  may 
  be 
  based 
  upon 
  

   some 
  interesting 
  figures 
  given 
  by 
  Blumcke 
  and 
  Hess 
  *. 
  

   From 
  the 
  rate 
  of 
  ablation 
  they 
  calculated 
  as 
  nearly 
  as 
  possible 
  

   the 
  volume 
  of 
  ice 
  that 
  was 
  passing 
  at 
  various 
  points 
  on 
  the 
  

   glacier. 
  They 
  then 
  assumed 
  that 
  the 
  velocity 
  was 
  the 
  same 
  

   at 
  the 
  bottom 
  as 
  at 
  the 
  surface, 
  and 
  found 
  the 
  thickness 
  of 
  

   the 
  glacier 
  at 
  various 
  points 
  on 
  this 
  assumption. 
  But 
  as 
  a 
  

   considerable 
  volume 
  of 
  ice 
  passes 
  down 
  owing 
  to 
  the 
  differ- 
  

   ential 
  motion 
  of 
  the 
  stream, 
  they 
  knew 
  that 
  the 
  ice 
  must 
  be 
  

   thicker 
  than 
  the 
  hypothetical 
  value 
  thus 
  obtained. 
  They 
  

   therefore 
  bored 
  through 
  the 
  glacier 
  at 
  various 
  points 
  and 
  

   found, 
  as 
  they 
  expected, 
  that 
  the 
  glacier 
  was 
  really 
  thicker. 
  

   The 
  following 
  Table 
  (11.) 
  gives 
  the 
  results 
  obtained 
  at 
  

   section 
  V. 
  

  

  

  Table 
  II. 
  

  

  

  B. 
  

  

  c. 
  

  

  Per 
  cent. 
  

  

  D. 
  

  

  139 
  

  

  310 
  

  

  4-31 
  

  

  424 
  

  

  19-0 
  

  

  8-05 
  

  

  45-2 
  

  

  19-0 
  

  

  8-59 
  

  

  461 
  

  

  40 
  

  

  1-84 
  

  

  417 
  

  

  310 
  

  

  1292 
  

  

  40-0 
  

  

  310 
  

  

  1460 
  

  

  325 
  

  

  100 
  

  

  3-20 
  

  

  7)5451 
  

  

  7*79 
  average 
  metres 
  

   per 
  annum. 
  

  

  Mitt. 
  d. 
  I) 
  u. 
  

  

  0. 
  A.-V.no. 
  4, 
  p. 
  46 
  (1905). 
  

  

  

  H 
  2 
  

  

  

  