PEOFESSOE  TYNDALL  ON  SOME  PHYSICAL  PEOPEETIES  OF  ICE. 
223 
heat  to  pass  through  it  by  conduction  is,  as  far  as  I know,  absolutely  null,  I was  glad  to 
avail  myself  of  an  opportunity  which  presented  itself  of  obtaining  some  approximate 
notion  of  this  power.  I owe  this  opportunity  to  the  kindness  of  Mr.  Harrison,  who 
had  de\ised  and  perfected  a machine  for  the  manufacture  of  ice  by  the  evaporation  of 
ether.  I first  examined  a mass  of  ice  of  the  shape  of  the  frustum  of  a cone.  The  dia- 
meter of  the  base  was  10^  inches,  of  the  top  7^  inches,  and  the  length  of  the  frustum 
was  2 feet.  During  the  freezing  of  this  mass  a thermometer  fixed  on  the  ice  showed  a 
temperature  of  8°  below  the  zero  of  Fahr.,  or  40°  of  Fahr.  below  the  freezing-point  of 
water. 
45.  Fourteen  hours  after  it  had  been  fi’ozen,  the  temperature  of  the  mass,  to  a depth 
of  2 inches  below  the  surface,  was  accurately  32°  Fahr.  At  the  heart  of  the  frustum 
the  temperature  was  31^°.  The  superficial  portions  of  the  frustum  had  been  the  coldest, 
and  we  see  that  in  fourteen  hours  the  ice  of  these  portions  rose  forty  degrees  in  tem- 
perature. 
46.  On  the  24th  of  April,  Mr.  Harrison  had  the  kindness  to  place  his  excellent 
machine  entirely  at  my  disposition.  The  vessel  which  contained  the  water  to  be  frozen 
was  shaped  like  the  inverted  frustum  of  a cone,  and  was  surrounded  by  a jacket,  between 
which  and  the  side  of  the  frustum  vaporized  ether  circulated ; the  whole  being  placed 
in  a vessel  of  water.  At  11  o’clock  a.m.,  1 placed  a thermometer  (A)  in  contact  with 
the  side  of  the  vessel,  and  about  2 inches  below  the  surface  of  the  water.  The  machine 
commenced  to  act,  an  opalescence  was  soon  observable  on  the  sides,  and  after  twenty 
minutes’  action  the  thermometer  was  firmly  imbedded  in  the  ice.  At  1 o’clock  p.m.,  a 
second  thermometer  (B),  placed  at  a distance  of  an  inch  from  the  side  of  the  frustum, 
was  also  surrounded  by  ice.  At  2^  20®  p.m.  a third  thermometer  (C)  was  placed  at  a 
distance  of  If  inch  from  the  side  of  the  vessel,  and  at  5'’  30®  p.m.  a fourth  thermo- 
meter (D)  was  placed  at  a distance  of  3 inches  from  the  side.  The  observed  tempera- 
tures of  these  thermometers  at  the  times  stated  are  given  in  the  following  Table : — 
At  8^  30®  p.m.  the  machine  w^as  stopped  and  the  supply  of  ether  was  cut  off.  The 
mercurial  columns  began  to  rise  gradually,  and  at  10  o’clock  p.m.  they  were  found  to 
be  as  follows : — 
A.  B.  C.  D. 
27°  27°  271°  281° 
