﻿88 
  Messrs. 
  K. 
  M. 
  Deeley 
  and 
  P. 
  H. 
  Parr 
  on 
  

  

  bars 
  were 
  cut 
  with 
  their 
  lengths 
  parallel 
  to 
  the 
  optic 
  axis 
  ; 
  

   the 
  torsion 
  shear 
  planes 
  were, 
  therefore, 
  at 
  right 
  angles 
  to 
  the 
  

   optic 
  axes. 
  Torsional 
  shear 
  of 
  this 
  nature 
  would 
  distort 
  

   the 
  planes 
  of 
  the 
  three 
  secondary 
  axes 
  of 
  the 
  crystals, 
  and 
  

   on 
  this 
  account 
  the 
  experiment 
  cannot 
  be 
  compared 
  with 
  the 
  

   1891 
  experiments 
  of 
  McConnell 
  on 
  the 
  shear 
  at 
  right 
  

   angles 
  to 
  the 
  optic 
  axes 
  of 
  single 
  ice 
  crystals. 
  Weinberg's 
  

   results 
  were 
  not, 
  in 
  these 
  cases, 
  obtained 
  with 
  wide 
  varia- 
  

   tions 
  of 
  stress, 
  and 
  we 
  are 
  therefore 
  without 
  information 
  

   as 
  to 
  the 
  variation 
  of 
  the 
  rate 
  of 
  shear 
  with 
  varying 
  stress 
  

   and 
  amount 
  of 
  distortion. 
  His 
  value 
  for 
  the 
  viscosity 
  of 
  

   torsional 
  shear 
  for 
  one 
  bar 
  he 
  tested 
  was 
  

  

  7] 
  = 
  1-244 
  xlO 
  13 
  poises. 
  

  

  Other 
  bars, 
  no 
  doubt 
  of 
  different 
  crystalline 
  structure, 
  

   gave 
  higher 
  viscosities. 
  

  

  Tn 
  1907 
  * 
  Weinberg 
  made 
  a 
  number 
  of 
  torsional 
  experi- 
  

   ments 
  with 
  bars 
  of 
  glacier 
  ice 
  and 
  gives 
  the 
  viscosity 
  as 
  

  

  7) 
  = 
  0-8 
  x 
  10 
  13 
  poises. 
  

  

  He 
  also 
  calculated 
  t 
  the 
  viscosity 
  of 
  the 
  ice 
  of 
  the 
  

   Hintereis 
  Glacier 
  (using 
  the 
  data 
  furnished 
  by 
  Bliimcke 
  and 
  

   Hess) 
  by 
  the 
  formula 
  given 
  by 
  Deeley 
  in 
  1895, 
  which, 
  

   however, 
  he 
  does 
  not 
  appear 
  to 
  have 
  seen. 
  He 
  obtained 
  

  

  V 
  = 
  (1-74 
  + 
  1-10) 
  x 
  10 
  13 
  poises. 
  

  

  In 
  1908 
  R. 
  M. 
  Deeley 
  J 
  made 
  some 
  calculations 
  of 
  the 
  

   viscosity 
  of 
  glacier 
  ice. 
  He 
  estimated 
  in 
  ten 
  instances 
  the 
  

   thickness 
  of 
  the 
  Mer 
  de 
  Glace, 
  the 
  Morteratsch, 
  the 
  Lower 
  

   Grindelwald, 
  and 
  the 
  Great 
  Aletsch 
  Glaciers. 
  Although 
  the 
  

   variations 
  in 
  the 
  calculated 
  viscosities 
  were 
  large, 
  the 
  mean 
  

   result, 
  which 
  may 
  be 
  somewhat 
  in 
  error, 
  was 
  

  

  v 
  = 
  7-89 
  X 
  10 
  13 
  poises. 
  

  

  He 
  also 
  estimated 
  § 
  from 
  McConnell's 
  experiments 
  the 
  

   viscosity 
  of 
  crystalline 
  ice 
  at 
  0° 
  C, 
  in 
  a 
  direction 
  at 
  right 
  

   angles 
  to 
  the 
  optic 
  axis, 
  and 
  found 
  it 
  to 
  be 
  about 
  

  

  7j 
  = 
  1 
  x 
  10 
  10 
  poises. 
  

  

  McConnell's 
  experiment 
  was 
  made 
  with 
  a 
  single 
  crystal, 
  

   and 
  this, 
  coupled 
  with 
  the 
  fact 
  that 
  the 
  shear 
  did 
  not 
  disturb 
  

   the 
  crystal 
  axes, 
  probably 
  accounts 
  for 
  the 
  viscosity 
  being- 
  

   much 
  smaller 
  than 
  that 
  obtained 
  by 
  Weinberg 
  in 
  his 
  torsion 
  

   experiments 
  in 
  1905. 
  

  

  * 
  Annalen 
  der 
  Physik, 
  Bd. 
  xxii. 
  Heft 
  2, 
  pp. 
  331-832 
  (1907). 
  

  

  t 
  Zeitschrift 
  fur 
  Gletscherkiinde, 
  1 
  Band 
  (1906-7), 
  5 
  Reft. 
  

  

  + 
  Proc. 
  Roy. 
  Soc. 
  A. 
  vol. 
  lxxxi. 
  pp. 
  250-259 
  (1908). 
  § 
  Ibid. 
  

  

  