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PEOrESSOE  TTNDAXL  ON  SOIME  PHTSICAE  PEOPEETIES  OF  ICE. 
revealed  itself.  Allowing  the  light  from  a window  to  fall  upon  the  ice  at  a suitable 
incidence,  the  interior  of  the  mass  was  found  filled  with  httle  fiower-shaped  figures. 
Each  flower  had  six  petals,  and  at  its  centre  was  a bright  spot,  which  shone  with  more 
than  metalhc  brilhancy.  The  petals  were  manifestly  composed  of  water,  and  were  con- 
sequently dim,  their  visibility  depending  on  the  small  difference  of  refrangibihty  between 
ice  at  32°  Fahe.  and  water  at  the  same  temperature. 
5.  For  a long  time  I found  the  relation  between  the  planes  of  these  flowers  and  the 
planes  of  freezing  perfectly  constant.  They  were  always  parallel  to  each  other.  The 
development  of  the  flowers  was  independent  of  the  direction  in  which  the  beam  traversed 
the  ice.  Hence,  when  an  mregular  mass  of  transparent  ice  was  presented  to  me,  by 
sending  a sunbeam  through  it,  I could  tell  in  an  instant  the  direction  in  which  it  had 
been  frozen. 
Allowing  the  beam  to  enter  the  edge  of  a plate  of  ice,  and  causing  the  latter  to  move 
at  right  angles  to  the  beam,  so  that  the  radiant  heat  traversed  difierent  portions  of  the 
ice  in  succession,  when  the  track  of  the  beam  was  observed  through  an  eye-glass,  the 
ice,  which  a moment  before  was  optically  continuous,  was  instantly  staiTed  by  those 
lustrous  little  bubbles,  and  around  each  of  them  the  formation  and  growth  of  its  asso- 
ciated flower  could  be  distinctly  observed. 
6.  The  maximum  effect  was  confined  to  a space  of  about  an  inch  from  the  place  at 
which  the  beam  first  struck  the  ice.  In  this  space  the  absorption,  which  resolved  the 
ice  into  liquid  flowers,  for  the  most  part  took  place,  but  I have  traced  the  effect  to  a 
depth  of  several  inches  in  large  blocks  of  ice. 
7.  At  a distance,  however,  from  the  point  of  incidence,  the  spaces  between  the  flowers 
became  greater ; and  it  was  no  uncommon  thing  to  see  flowers  developed  in  planes  a 
quarter  of  an  mch  apart,  while  no  change  whatever  was  observed  in  the  ice  between 
these  planes. 
8.  The  pieces  of  ice  experimented  on  appeared  to  be  quite  homogeneous,  and  their 
transparency  was  very  perfect.  Why  then  did  the  substance  yield  at  particular  pomts  I 
Were  they  really  weak  points  of  crystalline  structure,  or  did  the  pelding  depend  upon 
the  manner  in  which  the  calorific  wave  impinged  upon  the  molecules  of  the  body  at 
these  points  1 However  these  and  other  questions  may  be  answered,  the  experiments 
have  an  important  bearing  upon  the  question  of  absorption.  In  ice  the  absorption  of 
the  rays  which  produce  the  flowers  is  fitful,  and  not  continuous ; and  there  is  no  reason 
to  suppose  that  in  other  solids  the  case  is  not  the  same,  though  then-  constitution  may 
not  be  such  as  to  reveal  it*. 
I have  applied  the  term  “bubbles”  to  the  little  bright  disks  in  the  middle  of  the 
flowers,  simply  because  they  resembled  the  little  air-globules  entrapped  in  the  ice ; but 
whether  they  contained  ah’  or  not  could  only  be  decided  by  experiment. 
* Notwithstanding  the  incomparable  diathermaneity  of  the  substance,  M.  Kxoblatjch  finds  that  when 
plates  of  rock-salt  are  thick  enough,  they  always  exhibit  an  elective  absorption.  Eflects  like  those  above 
described  may  possibly  be  the  cause  of  this. 
