﻿94 
  Messrs. 
  R. 
  M. 
  Deeley 
  and 
  P. 
  H. 
  Parr 
  on 
  

  

  Changes 
  occur 
  from 
  time 
  to 
  time 
  in 
  the 
  velocity 
  of 
  glacier 
  

   flow. 
  These 
  changes 
  are 
  intimately 
  connected 
  with 
  their 
  

   varying 
  advances 
  and 
  retreats, 
  which 
  result 
  from 
  periodical 
  

   alterations 
  in 
  the 
  amounts 
  of 
  precipitation 
  and 
  ablation 
  or 
  

   other 
  causes. 
  During 
  retreats 
  of 
  the 
  glacier 
  snout 
  the 
  

   velocity 
  and 
  thickness 
  decrease, 
  whilst 
  during 
  its 
  advance 
  

   the 
  velocity 
  and 
  thickness 
  increase. 
  

  

  According 
  to 
  Bliimcke 
  and 
  Hess 
  the 
  maximum 
  speed 
  of 
  

   the 
  Hintereis 
  Glacier 
  at 
  section 
  III. 
  was 
  34*7 
  metres 
  in 
  

   1893-1894, 
  41-2 
  metres 
  in 
  1894-1895, 
  and 
  38"7 
  metres 
  per 
  

   annum 
  in 
  1895-1896. 
  This 
  shows 
  that 
  the 
  velocity 
  at 
  the 
  

   date 
  the 
  measurements 
  were 
  made, 
  1894-1895, 
  was 
  not 
  

   quite 
  that 
  of 
  the 
  " 
  steady 
  state." 
  The 
  velocity 
  corresponding 
  

   to 
  the 
  steady 
  state 
  occurs 
  at 
  some 
  time 
  between 
  a 
  period 
  of 
  

   maximum 
  and 
  minimum 
  velocity. 
  It 
  is 
  probable 
  that 
  the 
  

   velocity 
  taken 
  is 
  rather 
  too 
  great. 
  

  

  Our 
  knowledge 
  of 
  the 
  seasonal 
  variations 
  of 
  glacier 
  flow 
  is 
  

   by 
  no 
  means 
  complete. 
  The 
  first 
  reliable 
  observations 
  were 
  

   made 
  by 
  August 
  Balmat, 
  the 
  guide, 
  under 
  the 
  direction 
  of 
  

   J. 
  D. 
  Forbes 
  *, 
  on 
  the 
  Glacier 
  des 
  Bois, 
  Chamouni, 
  a 
  little 
  

   below 
  the 
  Chapeau, 
  opposite 
  the 
  Montanvert 
  Hotel, 
  at 
  about 
  

   one-third 
  of 
  the 
  breadth 
  of 
  the 
  glacier 
  on 
  its 
  eastern 
  side. 
  

   His 
  results 
  are 
  plotted 
  on 
  fig. 
  4. 
  

  

  The 
  observations 
  indicated 
  by 
  the 
  crosses 
  were 
  made 
  in 
  

   1884, 
  and 
  those 
  by 
  circles 
  in 
  1885. 
  Some 
  of 
  the 
  observa- 
  

   tions 
  made 
  in 
  October 
  and 
  November 
  are 
  considerably 
  greater 
  

   than 
  the 
  velocities 
  shown 
  by 
  the 
  smoothed 
  curve 
  ; 
  but 
  from 
  

   November 
  to 
  March 
  they 
  show 
  a 
  continuously 
  low 
  value. 
  

   This 
  curve 
  of 
  velocities 
  corresponds 
  very 
  closely 
  with 
  the 
  

   temperature 
  curve 
  for 
  the 
  same 
  period 
  at 
  Geneva. 
  

  

  Tyndall 
  made 
  some 
  observations 
  along 
  the 
  same 
  section 
  in 
  

   December 
  1859. 
  He 
  then 
  found 
  the 
  maximum 
  velocity 
  to 
  

   be 
  16 
  inches 
  per 
  diem. 
  This 
  agrees 
  fairly 
  well 
  with 
  the 
  

   velocity 
  found 
  by 
  Balmat, 
  viz. 
  14 
  inches 
  per 
  diem. 
  Tyndall, 
  

   however, 
  found 
  the 
  July 
  speed 
  to 
  be 
  33§ 
  inches, 
  whereas 
  

   Balmat 
  and 
  Forbes 
  made 
  it 
  50 
  inches. 
  

  

  In 
  the 
  summer, 
  no 
  doubt, 
  the 
  velocity 
  varies 
  considerably 
  

   according 
  to 
  the 
  state 
  of 
  the 
  weather; 
  but 
  in 
  the 
  winter, 
  

   when 
  the 
  ice 
  is 
  deeply 
  covered 
  with 
  snow, 
  the 
  conditions 
  

   would 
  be 
  more 
  equable. 
  

  

  From 
  fig. 
  4 
  the 
  mean 
  speed 
  is 
  found 
  to 
  be 
  28*5 
  inches 
  

   per 
  diem, 
  the 
  maximum 
  speed 
  abcut 
  50 
  inches 
  in 
  July 
  and 
  

   the 
  minimum 
  speed 
  14 
  inches 
  in 
  December 
  ; 
  the 
  maximum 
  

   speed 
  being 
  about 
  68 
  per 
  cent, 
  greater 
  than 
  the 
  mean 
  and 
  

   the 
  winter 
  rate 
  about 
  56 
  per 
  cent, 
  slower 
  than 
  the 
  mean. 
  

   * 
  ' 
  Theory 
  of 
  Glaciers/ 
  pp. 
  128-132. 
  

  

  