38         Canon  Moseley  on  the  Mechanical  Impossibility  of 
the  printing  instruments,  one  was  erected  in  July  at  the  new- 
laboratory  at  Eton  College ;  the  other,  made  for  Lord  Lindsay, 
has  not  yet  been  erected,  but  has  been  at  work  for  six  or  eight 
weeks  at  Mr.  Apps's.  In  the  last-named  instrument  a  clock-face 
has  been  placed  in  front  of  the  force  printing-magnet,  showing 
the  hour  being  printed;  and  a  lever-handle  with  a  catch  has 
been  added  for  pressing  down  the  spring  roller  beneath  the  hour^ 
wheel  for  the  purpose  of  introducing  new  papers  easily.  The 
reels  hold  a  supply  of  paper  for  three  or  four  months. 
Y.  On  the  Mechanical  Impossibility  of  the  Descent  of  Glaciers 
by  their  Weight  only.  By  Henry  Moseley,  Canon  of  Bris- 
tol, F.R.S.,  andCorresponding  Member  of  the  Institute  of  Finance, 
in  answer  to  Mr.  Mathews*. 
IN  order  that  the  question  of  the  possibility  of  the  descent  of 
glaciers  by  their  weight  only  may  be  discussed  as  one  of  exact 
science,  it  is  necessary  that  some  geometrical  form  be  assigned  to 
a  glacier.  I  have  assumed  the  simplest.  I  have  imagined  a  glacier 
having  a  uniform  rectangular  cross  section  of  equal  roughness, 
and  of  a  constant  slope  and  direction.  My  argument  is,  1st,  That 
it  is  impossible  such  a  glacier  should  descend  with  that  differen- 
tial motion  which  is  characteristic  of  the  descent  of  glaciers  by  its 
weight  only ;  2ndly,  That,  this  being  impossible  with  a  glacier  of 
a  uniform  section  and  constant  slope  and  direction,  it  is  impos- 
sible a  fortiori  with  an  actual  glacier  of  a  variable  slope,  section, 
and  direction. 
No  question  appears  to  me  to  have  been  raised  by  Mr.  Ma- 
thews and  the  other  gentlemen  who  have  done  me  the  honour  to 
answer  my  paper,  as  to  whether,  admitting  my  first  conclusion, 
the  second  necessarily  follows  from  it.  They  have  not  denied 
that  if  it  be  true  that  a  glacier  could  not  descend  by  its  weight 
in  my  imaginary  channel,  it  follows  a  fortiori  that  it  could  not 
descend  in  a  channel  such  as  the  actual  channels  of  glaciers  are. 
"What  I  propose  now  to  do  is  therefore  to  answer  their  objections 
(and  specially  those  of  Mr.  Mathews)  to  my  first  conclusion,  that 
in  a  uniform rectangularchannel of  constant  direction  and  of  a  con- 
stant slope  equal  to  that  of  the  Mer  de  Glace  it  is  impossible  that 
a  glacier  should  descend  by  its  weight  only.  Mr.  Mathews  will, 
I  think,  admit  that  in  the  descent  of  such  a  glacier  the  motions 
of  different  points  in  a  straight  line  drawn  across  its  surface  at 
right  angles  to  its  axis  would  be  different  but  parallel  to  one 
another,  like  those  of  the  surface  of  a  stream  of  water  flowing  in 
such  a  channel— and  that  they  would  be  different  and  parallel  to 
*  Communicated  by  the  Author. 
