﻿$6 
  Messrs. 
  R. 
  M. 
  Deeley 
  and 
  P. 
  H. 
  Parr 
  on 
  

  

  illustrating 
  the 
  nature 
  of 
  glacier 
  flow 
  ; 
  but 
  his 
  assumptions 
  

   were 
  not 
  satisfactory, 
  and 
  his 
  results 
  were 
  too 
  complex 
  to 
  be 
  

   of 
  any 
  practical 
  value. 
  The 
  conclusions 
  he 
  reached 
  can 
  be 
  

   easily 
  obtained 
  by 
  much 
  more 
  simple 
  methods. 
  

  

  In 
  1891 
  McConnell 
  * 
  made 
  further 
  experiments 
  on 
  the 
  

   shear 
  properties 
  of 
  ice. 
  He 
  found 
  that 
  an 
  ice 
  crystal 
  was 
  

   easily 
  sheared 
  without 
  fracture 
  along 
  planes 
  at 
  right 
  angles 
  

   to 
  the 
  optic 
  axis 
  ; 
  but 
  not 
  in 
  any 
  other 
  direction. 
  This 
  

   explained 
  some 
  of 
  the 
  results 
  McConnell 
  and 
  Kidd 
  had 
  

   previously 
  obtained, 
  among 
  which 
  may 
  be 
  mentioned 
  the 
  

   rigidity 
  under 
  stress 
  of 
  the 
  tensile 
  test-bar 
  the 
  optic 
  axis 
  of 
  

   which 
  was 
  at 
  right 
  angles 
  to 
  the 
  axis 
  of 
  the 
  bar, 
  and 
  also 
  

   the 
  very 
  small 
  yield 
  under 
  stress 
  of 
  a 
  bar 
  consisting 
  of 
  a 
  

   number 
  of 
  prisms 
  of 
  ice 
  with 
  their 
  optic 
  axes 
  parallel 
  with 
  

   the 
  axis 
  of 
  the 
  test-bar. 
  It 
  also 
  explained 
  why 
  the 
  test-bar 
  

   having 
  the 
  optic 
  axis 
  at 
  an 
  angle 
  of 
  45° 
  with 
  the 
  axis 
  of 
  the 
  

   test-bar 
  yielded 
  rapidly 
  and 
  continuously. 
  

  

  In 
  1895 
  R. 
  M. 
  Deeley 
  t 
  showed 
  that 
  the 
  details 
  of 
  glacier 
  

   flow, 
  so 
  far 
  as 
  was 
  then 
  known, 
  resembled 
  in 
  every 
  particular 
  

   the 
  flow 
  of 
  liquids 
  through 
  capillary 
  tubes. 
  In 
  such 
  tubes, 
  

   when 
  the 
  velocity 
  is 
  not 
  too 
  great, 
  the 
  flow 
  is 
  steady, 
  i. 
  e. 
  

   free 
  from 
  eddies. 
  Poiseuille 
  was 
  the 
  first 
  to 
  make 
  extensive 
  

   experiments 
  on 
  the 
  flow 
  of 
  liquids 
  through 
  capillary 
  tubes, 
  

   and 
  from 
  them 
  he 
  obtained 
  an 
  empirical 
  formula, 
  which 
  has 
  

   since 
  been 
  found 
  to 
  be 
  identical 
  with 
  that 
  obtained 
  by 
  mathe- 
  

   matical 
  analysis. 
  Deeley 
  showed 
  that 
  his 
  equations 
  could 
  

   be 
  applied 
  to 
  the 
  movements 
  of 
  glaciers. 
  They 
  are 
  as 
  

   follow 
  : 
  — 
  

  

  Maximum 
  velocity 
  = 
  — 
  (1) 
  

  

  where 
  P 
  is 
  the 
  bodily 
  force 
  producing 
  motion, 
  being 
  the 
  

   component 
  of 
  gravity 
  in 
  the 
  direction 
  of 
  movement, 
  b 
  the 
  

   thickness 
  of 
  the 
  ice, 
  and 
  77 
  its 
  viscosity. 
  

  

  Also 
  the 
  volume 
  passing 
  any 
  cross- 
  section 
  in 
  unit 
  of 
  time 
  

  

  =t 
  » 
  

  

  when 
  a 
  is 
  the 
  width 
  of 
  the 
  section. 
  

   For 
  a 
  semicircular 
  section 
  the 
  flux 
  

  

  7T 
  P£ 
  4 
  

  

  16' 
  77 
  

  

  * 
  Proc. 
  Koy. 
  Soc. 
  vol. 
  xlix. 
  pp. 
  323-34^ 
  

   t 
  Geol. 
  Mag. 
  Sept. 
  1895, 
  pp. 
  408-415. 
  

  

  (3) 
  

  

  