PEOFESSOE  TYNDALL  ON  SOME  PHYSICAL  PEOPEETIES  OF  ICE. 
219 
Norway  ice  with  Avhich  I experimented,  is  divided  into  segments  by  surfaces  of  discon- 
tinuity. The  air-  and  water-cavities  are  represented  as  flattened,  but,  as  in  the  lake  ice, 
they  seem  flattened  in  all  directions.  M.  Agassiz  regards  the  flattening  of  the  cavities 
as  a certain  proof  that  they  have  been  squeezed  flat  by  pressure ; and  he  attributes  the 
different  directions  of  flattening  to  a power  of  independent  motion  possessed  by  each 
fragment.  The  perfect  similarity,  however,  of  the  phenomena  presented  by  the  two 
kinds  of  ice  must  render  us  cautious  in  accepting  an  explanation  which  may  apply  to 
the  one,  but  excludes  the  other. 
§IV. 
30.  But  the  question  still  remains,  how  are  the  water-chambers  produced  within  the 
ice  ^ Mr.  Huxley  throws  out  the  suggestion,  which  our  knowledge  at  the  time  of  his 
observations  rendered  most  probable,  namely,  that  the  water  had  never  been  frozen  at 
all,  but  had  preserved  itself,  like  the  liquid  in  the  cavities  of  a Gruyere  cheese,  from 
the  neve  downwards. 
31.  One  simple  test  will,  I think,  decide  the  question  whether  the  liquid  is  or  is  not 
the  product  of  melted  ice.  If  it  be,  its  volume  must  be  less  than  that  of  the  ice  which 
produced  it,  and  the  bubble  associated  with  the  water  must  he  composed  of  rarefied  air. 
Hence,  if  on  establishing  a liquid  connexion  between  this  bubble  and  the  atmosphere  a 
diminution  of  volume  be  observed,  this  will  indicate  that  the  water  has  been  produced 
by  the  melting  of  the  ice. 
32.  From  a block  of  Norway  ice,  containing  such  compound  bubbles,  I cut  a prism, 
and  immersing  it  in  warm  water,  contained  in  a glass  vessel,  I carefully  watched  through 
the  side  of  the  vessel  the  effect  of  the  melting  upon  the  bubbles.  They  invariably 
shrunk  in  volume  at  the  moment  the  surroundiny  ice  was  melted,  and  the  diminished 
globule  of  air  rose  to  the  surface  of  the  water.  I then  arranged  matters  so  that  the 
wall  of  the  cavity  might  be  melted  away  underneath,  without  permitting  the  bubble  of 
air  at  the  top  to  escape.  At  the  moment  the  melting  reached  the  cavity  the  air-bubble 
instantly  collapsed  to  a sphere,  possessing,  in  some  cases,  far  less  than  the  hundredth  part 
of  its  original  volume.  The  experiments  were  repeated  with  several  distinct  masses  of 
ice,  and  always  with  the  same  result.  I think,  therefore,  it  may  be  regarded  as  certain 
that  the  liquid  cells  are  the  product  of  melted  ice*. 
33.  Consideiing  the  manner  in  which  ice  imported  into  this  country  is  protected  from 
the  solar  rays,  I think  we  must  infer  that  in  the  specimens  examined  by  mef,  the  ice  in 
contact  with  the  bubble  has  been  melted  by  heat  which  has  been  conducted  through  the 
substance  without  visible  prejudice  to  its  solidity. 
34.  Paradoxical  as  this  may  appear,  I think  it  is  no  more  than  might  reasonably  be 
expected  from  d priori  considerations.  The  heat  of  a body  is  referred,  at  the  present 
* This  of  course  refers  to  the  lake  ice  examined  as  described.  I venture  to  predict,  however,  that  the 
same  will  be  found  true  of  the  bubbles  in  glacier  ice. 
t And  in  those  portions  of  glacier  ice  which  are  withdrawn  from  the  direct  action  of  the  sun. 
2 G 2 
