﻿the 
  Viscosity 
  of 
  Glacier 
  Ice. 
  87 
  

  

  In 
  1897 
  L. 
  de 
  Marchi* 
  investigated 
  the 
  internal 
  move- 
  

   ments 
  of 
  glaciers, 
  and 
  made 
  some 
  calculations 
  which 
  appeared 
  

   to 
  show 
  an 
  agreement 
  between 
  theory 
  and 
  fact; 
  but 
  the 
  

   agreement 
  he 
  obtained 
  was 
  illusive, 
  for 
  he 
  had, 
  according 
  to 
  

   Weinberg, 
  misplaced 
  a 
  decimal 
  point 
  and 
  omitted 
  to 
  include 
  

   the 
  value 
  of 
  gravity 
  in 
  his 
  equations. 
  

  

  It 
  would 
  be 
  a 
  distinct 
  advantage 
  to 
  have 
  a 
  name 
  for 
  the 
  

   unit 
  of 
  viscosity 
  expressed 
  in 
  C. 
  Gr. 
  S. 
  units, 
  and 
  we 
  would 
  

   suggest 
  that 
  the 
  word 
  Poise 
  be 
  used 
  for 
  this 
  ; 
  for 
  it 
  is 
  to 
  

   Poiseuille 
  that 
  we 
  owe 
  the 
  experimental 
  demonstration 
  that 
  

   when 
  a 
  liquid 
  flows 
  through 
  a 
  capillary 
  tube 
  of 
  considerable 
  

   length, 
  at 
  constant 
  temperature, 
  the 
  viscosity 
  is 
  constant 
  at 
  

   all 
  rates 
  of 
  shear, 
  provided 
  that 
  the 
  flow 
  is 
  not 
  turbulent. 
  In 
  

   the 
  case 
  of 
  a 
  soft 
  solid 
  (plastic 
  substance) 
  the 
  so-called 
  

   viscosity 
  is 
  not 
  the 
  same 
  for 
  all 
  rates 
  of 
  shear 
  : 
  whereas 
  the 
  

   viscosity 
  of 
  a 
  liquid 
  is 
  a 
  physical 
  constant 
  f 
  and 
  should 
  be 
  

   named. 
  

  

  "We 
  have 
  seen 
  that 
  glacier 
  ice 
  consists 
  of 
  crystal 
  granules 
  

   which 
  not 
  only 
  shear 
  freely 
  along 
  planes 
  at 
  right 
  angles 
  to 
  

   the 
  optic 
  axis 
  ; 
  but 
  also 
  undergo 
  changes 
  at 
  their 
  bounding 
  

   surfaces 
  which 
  enable 
  the 
  mass 
  to 
  suffer 
  continuous 
  distortion 
  

   under 
  stress. 
  The 
  ability 
  of 
  glacier 
  ice 
  to 
  spread 
  out 
  into 
  

   piedments 
  whose 
  upper 
  surfaces 
  are 
  very 
  nearly 
  level 
  also 
  

   shows 
  that 
  such 
  shear 
  may 
  take 
  place 
  under 
  very 
  small 
  

   stresses. 
  Both 
  Main 
  and 
  McConnell 
  & 
  Kidd 
  found 
  that 
  test- 
  

   bars 
  of 
  glacier 
  ice 
  did 
  not 
  yield 
  in 
  a 
  regular 
  manner, 
  nor 
  

   was 
  the 
  rate 
  of 
  yield 
  always 
  quite 
  proportional 
  to 
  the 
  stress. 
  

   Other 
  experimentalists 
  have 
  also 
  noticed 
  this. 
  This 
  is 
  con- 
  

   sidered 
  to 
  arise 
  mainly 
  from 
  the 
  fact 
  that 
  the 
  glacier 
  grains 
  

   are 
  large 
  as 
  compared 
  with 
  the 
  size 
  of 
  the 
  test-bar, 
  and 
  

   that 
  the 
  yielding 
  is 
  due 
  to 
  inter 
  facial 
  movement 
  as 
  well 
  as 
  

   shear 
  in 
  the 
  granules. 
  

  

  As 
  compared 
  with 
  the 
  mass 
  of 
  a 
  glacier, 
  however, 
  the 
  

   granules 
  are 
  small, 
  and 
  they 
  may 
  even 
  more 
  nearly 
  be 
  

   compared 
  with 
  the 
  molecules 
  of 
  a 
  small 
  volume 
  of 
  such 
  a 
  

   liquid 
  as 
  oil. 
  But 
  even 
  though 
  the 
  viscosity 
  of 
  a 
  glacier 
  

   cannot 
  probably 
  be 
  considered 
  as 
  quite 
  the 
  same 
  thing 
  as 
  

   the 
  viscosity 
  of 
  water 
  and 
  other 
  mobile 
  liquids, 
  glacier 
  ice 
  

   may 
  yet, 
  for 
  all 
  practical 
  purposes, 
  be 
  regarded 
  as 
  a 
  perfect 
  

   liquid 
  of 
  high 
  viscosity. 
  It 
  will 
  flow 
  until 
  all 
  the 
  stresses 
  

   are 
  in 
  hydrostatic 
  equilibrium. 
  

  

  In 
  1905 
  Boris 
  Weinberg 
  + 
  made 
  some 
  torsion 
  experiments 
  

   on 
  the 
  stream 
  ice 
  of 
  the 
  Neva. 
  In 
  the 
  case 
  of 
  stream 
  ice 
  his 
  

  

  * 
  ' 
  ; 
  L'nttrito 
  interno 
  nel 
  movimente 
  du 
  ghiacciai." 
  licndic. 
  Id. 
  Lom- 
  

   bardo 
  (2) 
  vol. 
  xxx. 
  p. 
  284 
  (1897). 
  

  

  t 
  Osborne 
  Reynolds, 
  Phil. 
  Trans. 
  1836, 
  p. 
  160. 
  

  

  X 
  Annalen 
  der 
  Physik 
  (Leipzig), 
  Bd, 
  xviii. 
  Heft 
  1, 
  pp. 
  81-91 
  (1905). 
  

  

  