218 
PEOFESSOE  TYNDALL  ON  SOME  PHYSICAL  PEOPEETIES  OF  ICE. 
Such,  if  I mistake  not,  are  the  properties  of  radiant  heat  which  modem  physics  hare 
revealed ; and  I think  they  render  it  evident  that  the  hypothesis  of  M.  Agassiz  and  the 
Messrs.  Schlagintweit  was  accepted  without  due  regard  to  its  consequences. 
But  as  the  sun  does  reach  the  lower  strata  of  the  atmosphere,  it  may  be  thought  that 
we  are  protected  from  its  effects  by  the  radiation  from  the  air  neutralizing  its  absorp- 
tion. The  fact  however  is,  that  air  may  be  heated  to  an  intense  degree  without  showing 
any  measureable  amount  of  radiation.  The  hot  current  from  an  Ai-gand  chimney  pro- 
duces, according  to  Melloni,  no  sensible  effect  upon  a dehcate  thermo-electric  appa- 
ratus. Hence  it  is  not  because  the  air  gets  rid  of  its  heat  by  radiation,  but  simply 
because  its  power  of  absorption  is  infinitely  behind  that  supposed  by  the  h}*pothesis  of 
M.  Agassiz  and  the  Messrs.  Schlagintweit,  that  animal  and  vegetable  existence  at  the 
earth’s  surface  is  possible. 
When  air-bubbles  occurred  in  those  portions  of  the  ice  where  the  liquid  disks 
appeared,  the  associated  water  spread  out  on  planes  parallel  to  those  of  the  disks, 
evidently  in  consequence  of  the  freer  yielding  of  the  ice  in  these  planes.  Keeping  this 
remark  in  view  and  comparing  fig.  1 with  fig.  10,  plate  4 of  M.  Agassiz’  Atlas,  the 
resemblance  of  both  phenomena  will  at  once  be  perceived.  The  glacier  ice,  like  the 
compound,  I think  it  may  be  predicted  that  it  will  destroy  the  longer  undulations.  For  the  present  I will 
avoid  speculation  upon  this  subject,  and  confine  myself  to  facts.  If  we  examine  the  list  of  solid  substances 
whose  power  to  transmit  radiant  heat  instantaneously  have  been  examined  by  Mellosi,  we  find  that  those 
at  the  lower  end  of  the  list,  that  is,  the  most  imperfectly  diathermanous  substances,  all  contain  hydrogen. 
In  no  single  case,  where  this  element  occurs,  is  the  substance  capable  of  transmitting  rays  from  a source  of 
752°  Fahr.  ; while  in  every  case  where  it  does  not  occur,  the  power  of  transmitting  rays  from  this  source  is 
manifested  in  a greater  or  less  degree.  Amber,  gum,  citric  acid,  alum,  sugar-candy,  tartrate  of  potash  and 
soda,  are  the  substances  which  exercise  this  destructive  agency  upon  the  longer  undulations ; ice  being  the 
most  non-diathermanous  transparent  body  hitherto  examined.  Turning  to  Melloxi’s  list  of  liquids,  the 
same  fact  reveals  itself.  There  is  a sudden  fall  in  the  power  of  transmission  at  the  place  where  hydrogen 
enters  the  list.  Protochloride  of  phosphorus  transmits  62  per  cent,  of  the  rays  incident  upon  it,  but  the 
next  substance,  hydrocarhuret  of  chlorine,  transmits  only  37  per  cent.  From  this  point  to  the  end  of  the 
Table  the  substances  named  all  contain  hydrogen,  the  list  being  closed  by  distilled  ivater,  which  transmits 
only  11  per  cent,  of  the  calorific  rays  from  an  Argand  lamp. 
To  the  same  element,  I believe,  is  to  he  referred  the  difterence  between  Sir  AY.  Heeschel  and  Seebecr 
as  to  the  place  of  maximum  heat  in  the  solar  spectrum.  Heeschel  found  this  place  to  he  beyond  the  ex- 
treme red,  but  Seebeck,  with  a prism  of  sulphuric  acid,  found  it  to  be  in  the  orange,  while  with  a prism  of 
water  he  found  it  in  the  yellow.  Melloni  has  shown  that  this  is  due  to  the  destruction  of  the  less  refran- 
gible rays  by  the  two  liquids,  the  sulphuric  acid  being  regarded  by  him  as  acting  in  a manner  analogous  to 
water.  In  both  the  water  and  the  sulphuric  acid  used  by  Seebeck,  I believe  the  hydi’ogeu  to  be  the  agent 
which  gives  the  observed  character  to  the  results.  The  colour  of  ice  and  water  is  also  a necessary  conse- 
quence of  this  hostility  of  the  element  hydrogen  to  the  instantaneous  passage  of  the  longer  undulations. 
The  mathematical  theory  of  undulation  is,  perhaps,  perfect,  but  the  physics  of  the  process,  that  is,  the 
real  affections  of  light  and  heat  in  their  passage  through  bodies,  are  wholly  unknown  to  us.  Cases,  there- 
fore, like  the  foregoing,  which  single  out  a particular  substance  as  exhibiting  a special  department  towards 
light  and  heat,  are,  I think,  of  great  value.  Increased  knowledge  will  probably  enable  us  to  connect  these 
eftects  with  the  other  properties  of  this  substance,  and  tlms  establish  physical  relations  which  ai’e  now 
UTiknown  to  us. 
