224 
PEOFESSOE  TYNDALL  ON  SOME  PHYSICAL  PEOPEETIES  OF  ICE. 
The  machine  rested  throughout  the  night,  and  at  8 o’clock  on  the  morning  of  the  25th 
all  the  thermometers  stood  at  32°. 
47.  The  machine  was  set  going  at  8 a.m.  on  the  25th,  and  continued  working  until 
2 o’clock  in  the  afternoon,  its  office  now  bemg,  not  to  freeze,  hut  to  cool  the  ice  already 
frozen.  The  thermometers  were  read  off  every  quarter  of  an  hour,  but  it  is  not  neces- 
sary to  record  all  the  observations.  The  following  are  the  temperatures  noted  at  8 and 
11''  30"'  A.M.  and  at  2 p.m.: — 
Time. 
A. 
B. 
C. 
D. 
h m 
O 
O 
o 
o 
8 
32 
32 
32 
32 
11  30 
+ 1 
Hi 
23 
301 
2 
-11 
- 9 
-3 
- 1 
48.  At  2''  45'"  the  machine  was  stopped  and  the  supply  of  ether  cut  off.  The  upper 
surface  of  the  ice  was  covered  with  2 inches  of  hair-felt:  the  water  suiTounding  the 
frustum  audits  jacket  was  at  a temperature  of  32°;  the  thermometers  were  read  off 
every  half-hour,  but  I mil  limit  myself  at  present  to  a few  observations.  The  tempe- 
ratures at  2 o’clock  were  those  stated  at  the  close  of  the  last  Table. 
Time  of  observation. 
A. 
B. 
C. 
D. 
h m 
O 
0 
o 
O 
3 15  P.M. 
+11 
+ 9 
+ 6 
+ 2 
4 15 
18 
17 
14 
111 
5 15 
24 
221 
20 
18 
8 15 
281 
281 
271 
261 
11  15 
31 
301 
30 
291 
On  the  26  th  the  following  temperatures  were 
observed : — 
A. 
B. 
C. 
D. 
h m 
O 
0 
O 
O 
9 A.M. 
32 
31| 
311 
311 
1 30  P.M. 
32 
32 
31f 
311 
At  1*'  30*"  a hole  was 
bored  in 
the  centre  of  the  frustum  to  a 
depth  of  5 inches. 
in  this  another  thermometer  (E)  was  placed ; its  temperature  at  3''  30'"  p.m.  was  30^°. 
At  8 o’clock  in  the  morning  of  the  27th  the  observed  temperatures  were  the  following : — 
A. 
32° 
B. 
32° 
c. 
32° 
D. 
32° 
E. 
32° 
At  the  termination  of  the  experiment  the  water  surrounding  the  frustum  was  at  a 
temperature  of  36°  Fahe. 
49.  These  experiments  show,  that  however  bad  the  conducting  power  of  ice,  in  com- 
parison with  other  substances,  may  be,  the  assumption  that  blocks  of  it  which  have  been 
preserved  in  this  country  through  months  of  summer  weather  should  still  possess  a 
magazine  of  cold  beyond  that  due  to  a temperature  of  32°,  is  wholly  imcompatible  with 
the  physical  character  of  the  substance. 
