84  M.  E.  Edlund's  Researches  on  the  Electromotive 
gation  or  modification  of  the  position  of  the  molecules  at  the 
surface  of  contact.  The  intensity  of  the  thermoelectric  force 
in  the  contact  of  two  different  metals  depends,  to  a  high  degree, 
on  the  molecular  condition  of  the  metals.  If  that  condition 
undergo  a  modification  (as,  for  example,  by  tension,  compression, 
&c),  the  result  is  also  a  modification  in  the  thermoelectric  force. 
Now  we  know  that,  if  one  of  the  points  of  the  soldering  of  a 
thermoelectric  ring  be  heated,  we  obtain,  for  a  determinate  dif- 
ference of  temperature  between  the  surfaces  of  union,  a  current 
of  given  amount,  which  remains  constant  as  long  as  the  respec- 
tive temperatures  of  those  surfaces  remain  unchanged.  If,  now, 
the  metals  underwent  a  molecular  modification  at  the  hotter 
point  of  contact  (where  the  heat  is  absorbed),  the  current  could 
not  preserve  a  constant  force,  in  consequence  of  that  molecular 
modification ;  but  as  this  is  the  case,  it  follows  that  no  sensible 
molecular  modification  can  take  place  there.  We  must  therefore, 
in  order  to  give  an  adequate  explanation  of  the  disappearance  of 
the  heat,  admit  that  it  is  changed  into  another  form  of  motion ; 
and  of  all  those  with  which  we  are  acquainted,  electricity  is  the 
only  one  that  can  here  betaken  into  consideration. 
The  proof  given  by  me,  in  the  work  mentioned,  of  the  pre- 
sence of  an  electromotive  force  in  the  contact  between  metals,  is 
not  founded  on  a  mere  hypothesis,  but  on  facts  demonstrated  by 
experiment ;  the  result  obtained  (namely,  the  presence  of  an 
electromotive  force  at  the  surface  of  contact,  as  the  only  possible 
explanation  of  Peltier's  phenomena)  must  therefore  be  correct. 
This  force  transforms  heat  into  electricity.  It  does  not  create  the 
electric  motion  out  of  nothing,  but,  I  repeat,  changes  heat  into 
electricity.  The  electric  motion  produced  is  the  mechanical 
equivalent  of  the  heat  which  has  vanished.  If  heat  did  not 
exist  at  the  surface  of  contact,  the  rise  of  an  electric  current 
would  be  impossible ;  for  (if  I  may  so  express  myself)  the  mate- 
rials for  the  production  of  electricity  would  be  wanting.  The 
force  of  contact  resembles  in  this  respect  the  inductive  force 
which,  when  a  closed  circuit  is  brought  near  a  galvanic  current, 
transforms  into  an  induced  galvanic  current  the  mechanical 
work  necessary  to  produce  the  nearness. 
It  has  been  maintained*  that  the  contact  of  chemically  indif- 
ferent bodies  could  only  produce  a  galvanic  current  of  momen- 
tary, not  of  long  duration.  "  It  may  be  admitted,"  it  has  been 
said,  "  that,  in  the  approach  of  two  metals,  the  particles  are  mu- 
tually attracted,  move  rapidly  against  each  other,  and  at  length 
lose,  at  their  mutual  contact,  their  acquired  velocity.  The  vis 
viva  thus  lost  might  be  changed  into  electrical  decomposition  of 
*  Wiedemann,  Die  Lehre  vorn  Galvanismus  und  Erdmagnetismus,  part  ii. 
|  849;  Qf.  Helmholtz,  Erhaltung  der  Kraft. 
