﻿the 
  Viscosity 
  of 
  Glacier 
  Ice. 
  95 
  

  

  In 
  the 
  case 
  of 
  the 
  Hintereis 
  Glacier, 
  according 
  to 
  Finster- 
  

   walder*, 
  the 
  summer 
  velocity 
  for 
  1900 
  was 
  only 
  15 
  percent, 
  

   greater 
  than 
  the 
  average 
  velocity 
  for 
  the 
  two 
  years 
  1899- 
  

   1901. 
  The 
  greater 
  difference 
  between 
  the 
  mean 
  and 
  summer 
  

   velocity 
  of 
  the 
  Glacier 
  des 
  Bois 
  than 
  that 
  of 
  the 
  Hintereis 
  

   Glacier, 
  may 
  be 
  due 
  to 
  the 
  fact 
  that 
  the 
  former 
  is 
  only 
  

   1900 
  lr.etres 
  above 
  sea-level, 
  whereas 
  the 
  latter, 
  at 
  section 
  V., 
  

   is 
  2600 
  metres 
  above 
  the 
  sea, 
  and 
  the 
  heat 
  of 
  summer 
  has 
  

   less 
  influence. 
  

  

  Great 
  interest 
  attaches 
  to 
  the 
  winter 
  velocity. 
  We 
  must 
  

   assume 
  that 
  when 
  during 
  the 
  winter 
  the 
  ice 
  is 
  covered 
  with 
  

   snow 
  some 
  of 
  the 
  water 
  in 
  the 
  ice 
  congeals. 
  We 
  thus 
  during 
  

   the 
  winter 
  have 
  the 
  glacier 
  more 
  nearly 
  approaching 
  the 
  

   dry 
  state. 
  

  

  The 
  actual 
  winter 
  velocity 
  of 
  the 
  Hintereis 
  Glacier 
  does 
  

  

  not 
  appear 
  to 
  have 
  been 
  measured. 
  Even 
  in 
  the 
  case 
  of 
  the 
  

  

  summer 
  velocity 
  it 
  is 
  not 
  clear 
  whether 
  Finsterwalder's 
  

  

  measurement 
  gives 
  the 
  mean 
  summer 
  or 
  maximum 
  summer 
  

  

  velocity. 
  It 
  is 
  most 
  probably 
  the 
  maximum. 
  Compared 
  

  

  with 
  the 
  Glacier 
  des 
  Bois 
  the 
  winter 
  velocity 
  of 
  the 
  Hinte- 
  

  

  5 
  (i 
  x 
  15 
  

   reis 
  Glacier 
  would 
  be 
  . 
  , 
  ' 
  =12*3 
  per 
  cent, 
  less 
  than 
  the 
  

  

  mean 
  annual 
  velocity. 
  This 
  makes 
  the 
  winter 
  velocity 
  

   42'1 
  metres 
  per 
  annum. 
  We 
  thus 
  have 
  for 
  the 
  maximum 
  

   velocity 
  of 
  the 
  Hintereis 
  Glacier 
  

  

  Winter 
  velocity 
  12 
  "1 
  metres 
  per 
  annum. 
  

  

  Mean 
  annual 
  velocity 
  ... 
  48*0 
  „ 
  ,, 
  

  

  Summer 
  velocity 
  552 
  „ 
  ,, 
  

  

  Slip. 
  — 
  One 
  of 
  the 
  most 
  important 
  and 
  difficult 
  values 
  to 
  

   ascettain 
  is 
  the 
  amount 
  of 
  slip 
  which 
  takes 
  place 
  between 
  

   the 
  ice 
  and 
  the 
  rock-bed 
  upon 
  which 
  it 
  rests. 
  There 
  are 
  

   several 
  ways 
  of 
  estimating 
  this. 
  That 
  glaciers 
  do 
  slip 
  very 
  

   considerably 
  upon 
  their 
  beds 
  is 
  proved 
  by 
  the 
  striations, 
  

   grooving, 
  and 
  polishing 
  which 
  are 
  found 
  upon 
  rock 
  surfaces 
  

   over 
  which 
  glaciers 
  have 
  passed. 
  That 
  they 
  are 
  abrading 
  

   their 
  beds 
  is 
  also 
  shown 
  by 
  the 
  rock 
  flour 
  and 
  boulders 
  with 
  

   which 
  the 
  streams 
  issuing 
  from 
  the 
  ice 
  are 
  loaded. 
  

  

  At 
  the 
  edges 
  of 
  glaciers 
  the 
  ice 
  is 
  almost 
  always 
  found 
  to 
  

   be 
  in 
  motion. 
  In 
  the 
  case 
  of 
  the 
  Hintereis 
  Glacier 
  the 
  

   marginal 
  velocity, 
  near 
  section 
  V., 
  is 
  about 
  12 
  metres 
  per 
  

   annum, 
  or 
  25 
  per 
  cent, 
  of 
  the 
  maximum, 
  and 
  increases 
  very 
  

   rapidly 
  for 
  the 
  first 
  fifty 
  or 
  sixty 
  metres 
  from 
  the 
  edge. 
  

   This 
  rapid 
  increase 
  may 
  be 
  due 
  to 
  the 
  fact 
  that, 
  at 
  its 
  i 
  

  

  * 
  Hans 
  Hess, 
  < 
  Die 
  Gletscher/ 
  p. 
  2"0. 
  

  

  