274         M.  E.  Edlund's  Researches  on  the  Electromotive 
scope  is  a  measure  of  the  resultant  of  these  three  forces  ;  it  is 
therefore  not  a  result  of  the  metallic  contact  exclusively,  but  of 
all  three  combined ;  and  we  ought  not  to  be  surprised  that  the 
two  series  do  not  mutually  agree.  It  is  not  a  new  fact  that 
gases  condensed  at  the  surface  of  metals  exercise  an  influence  on 
electroscopic  experiments.  As  I  have  mentioned  above,  this 
fact  has  been  urged  as  an  objection  to  the  correctness  of  the 
contact  theory.  But  the  amount  of  this  influence  only  became 
fully  evident  when  the  true  electromotive  series  was  established 
as  it  comes  out  from  metallic  contact  only. 
From  the  preceding  we  are  fully  authorized  to  formulate  the 
following  propositions : — 
1.  As  established  by  electroscopic  experiments,  the  electric-ten- 
sion series  presents  no  immediate  relation  with  the  electromotive 
forces  at  the  contact  of  metals;  therefore  it  is  impossible  to  deter- 
mine from  that  series  the  amount  or  the  nature  of  those  forces. 
The  following  proposition  is  an  immediate  consequence  of  the 
preceding : — 
2.  The  order  of  the  metals  is  perfectly  identical  in  the  electro- 
motive and  in  the  thermoelectric  series  respectively. 
The  identity  of  the  two  series  indicates  an  intimate  connexion 
between  the  electromotive  and  thermoelectric  forces.  The  elec- 
tromotive forces  of  contact  transform  heat  into  electricity.  At 
the  absolute  zero  of  heat,  supposing  that  point  to  have  an  actual 
existence,  it  would  be  impossible  for  those  forces  to  produce 
electric  motion.  In  this  circumstance  we  arrive  spontaneously 
at  the  supposition  that  the  power  of  these  forces  to  occasion  an 
electric  motion  depends  on  the  quantity  of  heat  present,  or,  in 
other  words,  that  it  is  a  function  of  the  temperature.  In  fact 
Le  Roux  has  verified  this  by  experiment.  He  found  that  the 
quantity  of  heat  produced  or  absorbed  when  a  galvanic  current 
circulates  through  the  point  of  contact  between  bismuth  and 
copper  is  greater  at  the  temperature  of  -f  100°  than  when  the 
experiment  takes  place  at  the  ordinary  temperature.  The  elec- 
tromotive force  resulting  from  the  contact  between  bismuth  and 
copper  is  therefore  greater  at  the  former  temperature  than  at  the 
latter.  Let  us  suppose  several  metals  A,  B,  C,  &c.  soldered  to 
one  another  in  a  ring :  the  sum  of  the  electromotive  forces  will 
be  equal  to  0  when  the  temperature  is  the  same  at  all  the  sol- 
dering-points ;  if,  on  the  contrary,  the  temperature  be  augmented 
at  one  of  these  points,  a  thermoelectric  current  will  result.  This 
comes  from  the  electromotive  force  having  been  modified  by  the 
increase  of  temperature.  Thermoelectric  currents  therefore  con- 
stitute a  measure  of  the  modification  undergone  by  the  electro- 
motive force  when  the  temperature  is  raised  or  lowered. 
In  the  experiments  related  above  it  was  shown  that,  at  the 
