198  '    On  Breakage  of  Glass  Vessels.  {^Vayl'mh"' 
once  measured  in  glass  graduates  and  returned  to  the  water  bath,  and 
the  graduate  raay  be  washed  and  used  for  any  other  purpose  imme- 
diately. This  much  I  know,  but  in  regard  to  the  explanation  my 
mind  is  not  by  any  means  so  clear. 
On  first  applying  the  principle,  the  idea  presented  itself  that  the 
result  was  due  to  the  conduction  of  heat  by  the  metallic  rod.  It 
would  have  been  easy  to  account  for  the  circumstances  in  this  way, 
were  it  not  for  two  facts.  First,  the  rod  when  held  in  the  hand  at  a 
distance  from  the  bottle,  does  not  appear  to  become  heated  ;  and 
secondly,  the  liquid  in  the  bottle  continues  hot.  These  circumstances 
led  me  to  look  for  some  other  cause,  and  induced  me  to  engage  in  a 
series  of  experiments,  with  a  view  of  ascertaining  the  cause  of  the 
phenomenon. 
[The  author  proves  by  careful  experiments  that  neither  heat  nor 
electricity  is  conducted  off  through  the  metallic  rod,  and  then  pro- 
ceeds :] 
Experiment  XIII.  Placed  ten  cold  bottles  in  a  row  and  filled  them 
with  boiling  water,  using  the  same  7'od  every  time.  I  noticed  that  the 
sixth  bottle  broke,  and  after  that  two  more  of  the  four.  On  removing 
the  rod  from  the  last  bottle,  I  observed  that  where  it  had  been  in  the 
bottles  it  had  become  very  hot.    This  led  me  to  think  of 
Experiment  XIV.  Took  three  good,  wide-m.outhed,  pint  bottles, 
cooled  them  by  immersion  in  cold  water  (40°  F.)  for  twenty  minutes. 
Placed  on  the  bottom  of  a  tinned  iron  vessel  a  rod  of  iron,  filled  the 
vessels  with  water,  caused  it  to  boil  with  the  rod  in  it,  allowed  it  to 
boil  for  ten  minutes,  so  as  to  have  the  rod  and  water  of  the  same 
temperature  ;  took  out  the  rod  and  placed  it  in  one  of  the  bottles,  and 
poured  boiling  water  down  the  rod  into  the  bottle  ;  proceeded  in  the 
same  way  with  the  other  bottles.  Two  of  the  three  bottles  were 
broken.  These  experiments  showed  me,  that  after  a  rod  has  absorbed 
a  certain  amount  of  heat  it  is  of  little  or  no  avail. 
Experiment  XV.  Filled  a  cold  bottle  with  boiling  water,  using  a 
rod  of  iron  ;  cooled  the  bottle,  placed  the  r,^)d  in  water  and  boiled  it. 
After  one  hour  placed  the  hot  rod  in  the  same  bottle  and  poured  in 
boiling  water  as  before.  The  bottle  was  broken.  These  experiments 
led  me  to  the  conclusion  that  the  effect  is  due  to  the  cooling  effect 
upon  the  first  portions  of  the  water  caused  by  the  absorption  of  heat 
from  the  w:*ter  by  the  rod.  These  first  portions  of  the  water  being 
considerably  cooled  by  their  passages  down  the  cold  surface  of  the 
