222 
PEOPESSOE  TYNDALL  ON  SOIME  PHYSICAL  PEOPEETIES  OP  ICE. 
additional  temperature  necessary  to  overcome  the  resistance  to  liquefaction,  arising  from 
the  action  of  the  molecules  upon  each  other. 
42.  Now  let  us  suppose  two  pieces  of  ice  at  32°,  with  moistened  surfaces,  to  be 
brought  into  contact  with  each  other,  we  thereby  virtually  transfer  the  touching  po'iiions 
of  these  pieces  from  the  surface  to  the  interior^  where  32-j-a‘  is  the  melting  temperature. 
Liquefaction  will  therefore  be  arrested  at  those  sui’faces.  Before  being  brought  toge- 
ther, the  surfaces  had  the  motion  of  liquidity,  but  the  interior  of  the  ice  has  not  this 
motion ; and  as  equilibrium  will  soon  set  in  between  the  masses  on  each  side  of  the 
liquid  film  and  the  film  itself,  the  film  will  be  reduced  to  a state  of  motion  inconsistent 
with  liquidity.  In  other  words,  it  becomes  frozen  and  cements  the  two  suifaces  of  ice 
between  which  it  is  enclosed*. 
If  I am  right  here,  the  importance  of  the  physical  principles  involved  are  sufficiently 
manifest : if  I am  wi’ong,  I hope  I have  so  expressed  myself  as  to  render  the  detection 
of  my  error  easy.  Bight  or  wrong,  my  aim  has  been  to  give  as  explicit  utterance  to  my 
meaning  as  the  subject  will  admit  of. 
§ V. 
43.  Mr.  Faraday’s  experiments  on  the  freezing  together  of  pieces  of  ice  at  32°  Fahe., 
and  all  of  those  recounted  in  the  paper  published  by  Mr.  Huxley  and  myself,  find  then- 
explanation  in  the  principles  here  laid  down.  The  conversion  of  snow  into  neve,  and  of 
neve  into  glacier,  is  perhaps  the  grandest  illustration  of  the  same  principle  f.  It  has 
been,  however,  suggested  to  me  that  the  sticking  together  of  two  pieces  of  ice  may  be 
an  act  of  cohesion,  similar  to  that  which  enables  pieces  of  wetted  glass,  and  other  similar 
bodies,  to  stick  together.  This  is  not  the  case.  There  is  no  shding  motion  possible  to 
the  ice.  When  contact  is  broken,  it  breaks  with  the  snap  due  to  the  rupture  of  a solid. 
Glass  and  ice  cannot  be  made  to  stick  thus  together,  neither  can  glass  and  glass,  nor 
alum  and  alum,  nor  nitre  and  nitre,  at  common  temperatures.  I have,  moreover,  placed 
pieces  of  ice  together  overmight  and  found  them  in  the  morning  so  rigidly  frozen  toge- 
ther, that  when  I sought  to  separate  them,  the  surface  of  fracture  passed  thi-ough  one  of 
them  in  preference  to  taking  the  surface  of  regelation.  Many  sagacious  persons  ha-s  e 
also  suggested  to  me  that  the  ice  transported  to  this  country  from  Noi-way  and  the 
Wenham  Lake  may  possibly  retain  a residue  of  its  cold,  sufficient  to  freeze  a thhi  film 
enclosed  between  two  pieces  of  the  substance.  But  the  facts  already  adverted  to  are  a 
sufficient  reply  to  this  surmise.  The  ice  experimented  on  cannot  be  regarded  as  a 
magazine  of  cold,  because  parcels  of  liquid  water  exist  within  it. 
44.  Nevertheless,  as  our  present  knowledge  of  the  facility  with  which  ice  permits 
* It  is  here  implied  that  the  contact  of  the  moist  surfaces  must  be  so  perfect,  or  iu  other  words,  the 
liquid  film  between  them  must  he  so  thin,  as  to  enable  the  molecules  to  act  upon  each  other  across  it.  The 
extreme  tenuity  of  the  film  may  be  inferred  from  this.  A thick  plate  of  water  within  the  ice  would  facilitate 
rather  than  retard  liquefaction. 
t On  this  point  see  the  paper  referred  to  at  the  commencement. 
