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XII.  On  Glacier -motion. 
By  Edward  Vansittart  Neale,  Esq. 
To  the  Editors  of  the  Philosophical  Magazine  and  Journal. 
Gentlemen, 
IT  appears  to  me  that  Canon  Moseley  has  overlooked,  in  his 
valuable  researches  into  the  cause  of  the  movement  of  gla- 
ciers, two  considerations,  both  important,  if  I  am  not  mistaken, 
in  reference  to  that  question,  namely : — 1st,  the  accumulation  of 
pressure  to  which  the  lower  part  of  a  glacier  must  be  exposed 
from  the  mass  of  ice  behind  tending  to  thrust  it  forwards; 
2nd,  the  mode  in  which  ice  is  formed. 
1st.  If  we  imagine  a  glacier  to  be  divided,  transversely,  into 
sections  of  any  assumed  breadth,  say  one  foot  each,  and  suppose 
one  of  these  sections  placed  on  the  bed  of  the  glacier  by  itself, 
the  force  urging  any  particle  of  ice  on  the  lower  surface  of  the 
section  forwards  will,  I  conceive,  be  the  weight  of  the  whole 
mass  of  ice  above  and  behind  this  particle,  multiplied  into  the 
sine  of  the  angle  forming  the  slope  of  the  glacier-bed.  Now  sup- 
pose a  second  section  of  equal  breadth  placed  below  the  first,  so 
that  the  upper  face  of  this  section  shall  be  in  contact  with  the 
lower  face  of  the  first  section ;  the  particles  in  this  upper  face 
must  experience  the  same  amount  of  forward  thrust  as  those  of 
the  lower  face  with  which  they  are  in  contact.  Consequently 
the  particles  in  the  lower  face  of  the  second  section  will  be  sub- 
ject to  this  thrust,  in  addition  to  that  arising  from  the  weight  of 
the  mass  of  ice  in  their  own  division ;  and  thus,  when  any  con- 
siderable length  of  ice  is  acting  upon  a  slope,  a  pressure  may  be 
produced  upon  the  particles  of  ice  in  its  lowest  extremity  suffi- 
cient to  overcome  their  adhesion  to  each  other.  Hence  the  glacier 
would  yield  in  the  line  of  least  resistance — that  is,  in  the  direc- 
tion of  its  length.  The  accumulated  pressure  of  the  rear  ranks 
of  particles  would  set  the  front  ranks  in  motion,  and  these,  in 
turn,  would  drag  after  them  the  particles  in  their  rear  by  their 
molecular  adhesion;  so  that  a  glacier  might  "get  under  weigh" 
simply  by  its  own  weight — though,  if  glaciers  were  masses  of  ice 
of  definite  extent,  the  result  of  this  motion  would  probably  be 
only  to  split  it  up  into  fragments  where  the  retarding  and  im- 
pelling forces  were  evenly  balanced,  which  would  therefore 
again  become  stationary.  But  a  glacier  is  not  such  a  limited 
mass.  It  has  an  unlimited  reserve  of  power  in  the  snow  of  the 
mountain  height  whence  it  takes  its  origin,  into  which  it  gra- 
dually passes  as  its  course  is  traced  upwards.  Its  lower  parts 
can  never  stop ;  for  if  they  did,  the  store  of  power  supplied  by 
the  freely  moving  masses  of  what  in  Savoy  is  called  neve  would 
