﻿the 
  Viscosity 
  of 
  Glacier 
  Ice. 
  89 
  

  

  In 
  1910 
  Weinberg 
  *, 
  following 
  a 
  criticism 
  of 
  bis 
  figures 
  

   by 
  Hess, 
  gave 
  a 
  corrected 
  value 
  

  

  v 
  = 
  (l-75±0'70) 
  x 
  10 
  13 
  poises. 
  

  

  In 
  1912 
  R. 
  M. 
  Deeley 
  f 
  considered 
  tbe 
  results 
  obtained 
  

   by 
  Dr. 
  Main 
  in 
  his 
  tension 
  experiments, 
  and 
  obtained 
  

  

  rj 
  = 
  6 
  x 
  10 
  12 
  poises 
  

  

  for 
  the 
  viscosity 
  at 
  0° 
  C. 
  of 
  fine 
  crystalline 
  ice 
  frozen 
  in 
  an 
  

   iron 
  mould. 
  The 
  individual 
  experiments 
  showed 
  very 
  con- 
  

   siderable 
  differences 
  ; 
  the 
  figures 
  taken 
  are 
  the 
  mean 
  at 
  0° 
  C, 
  

   being 
  obtained 
  by 
  plotting 
  the 
  individual 
  results 
  on 
  a 
  

   diagram. 
  

  

  Although 
  the 
  experiments 
  by 
  McConnell 
  J 
  and 
  Kidd, 
  

   made 
  in 
  1888, 
  are 
  of 
  considerable 
  interest 
  and 
  were 
  carried 
  

   out 
  with 
  skill 
  and 
  accuracy, 
  they 
  have 
  not 
  hitherto 
  been 
  

   mathematically 
  examined. 
  

  

  They 
  showed 
  that 
  a 
  clear 
  bar 
  of 
  ice, 
  cut 
  out 
  of 
  a 
  single 
  ice 
  

   crystal, 
  with 
  the 
  optic 
  axis 
  at 
  right 
  angles 
  to 
  the 
  length 
  of 
  

   the 
  bar, 
  did 
  not 
  yield 
  appreciably 
  to 
  tension. 
  Another 
  bar, 
  

   having 
  the 
  optic 
  axis 
  parallel 
  with 
  the 
  length 
  of 
  the 
  bar, 
  also 
  

   failed 
  to 
  lengthen 
  very 
  appreciably 
  under 
  tensile 
  stress. 
  On 
  

   the 
  other 
  hand, 
  a 
  bar 
  having 
  the 
  optic 
  axes 
  of 
  its 
  numerous 
  

   long 
  crystals 
  inclined 
  at 
  an 
  angle 
  of 
  45° 
  lengthened 
  con- 
  

   tinuously 
  under 
  stress. 
  Taking 
  the 
  mean 
  result 
  for 
  their 
  

   experiments, 
  given 
  in 
  their 
  table 
  on 
  page 
  362 
  §, 
  we 
  obtain 
  a 
  

   viscosity 
  of 
  

  

  2±'8 
  X 
  10 
  12 
  poises. 
  

  

  Since 
  the 
  yield 
  must 
  have 
  been 
  at 
  right 
  angles 
  to 
  the 
  optic 
  

   axes, 
  the 
  high 
  viscosity 
  may 
  be 
  partly 
  due 
  to 
  the 
  low- 
  

   temperature 
  (about 
  — 
  5° 
  C), 
  to 
  the 
  fact 
  that 
  the 
  bar 
  con- 
  

   sisted 
  of 
  a 
  large 
  number 
  of 
  crystalline 
  columns, 
  and 
  that 
  the 
  

   shear 
  planes 
  were 
  inclined 
  to 
  the 
  direction 
  of 
  the 
  stress. 
  

  

  Several 
  tensile 
  experiments 
  were 
  also 
  made 
  with 
  glacier 
  

   ice. 
  McConnell 
  and 
  Kidd 
  || 
  remark 
  (p. 
  333) 
  : 
  " 
  We 
  tested 
  

   three 
  pieces, 
  which 
  were 
  quite 
  sufficient 
  to 
  disprove 
  the 
  

   common 
  notions 
  that 
  glacier 
  ice 
  is 
  only 
  plastic 
  under 
  pres- 
  

   sure, 
  not 
  under 
  tension, 
  and 
  that 
  regelation 
  is 
  an 
  essential 
  

   part 
  in 
  the 
  process." 
  These 
  three 
  pieces 
  were 
  composed 
  of 
  a 
  

   number 
  of 
  crystals 
  varying 
  in 
  thickness 
  from 
  two 
  to 
  three 
  

   millimetres 
  up 
  to 
  thirty 
  or 
  even 
  a 
  hundred. 
  These 
  crystals 
  

  

  * 
  Zeitschrift 
  fur 
  Gletscherkunde, 
  iv. 
  p. 
  380 
  (1909-10). 
  

   t 
  Geol. 
  Macr., 
  Decade 
  v, 
  vol. 
  ix. 
  pp. 
  265-9 
  (1912). 
  

   1 
  Proc. 
  Boy. 
  Soc. 
  vol. 
  xliv. 
  pp. 
  331 
  -367 
  (1888). 
  

   § 
  Proc. 
  Roy. 
  Soc. 
  vol. 
  xliv. 
  1888. 
  || 
  Ibid. 
  

  

  