Force  in  the  Contact  of  Metals. 
223 
can  therefore  deduce  the  former  from  the  latter,  and  thus  obtain 
the  value  of  a  for  those  combinations  in  respect  of  which  it  has 
not  been  directly  determined.  In  this  way  we  find,  for  the 
combinations : — 
Iron-copper  ....  1-42  «,= 127-06 
Cadmium-copper  .  .  .  „  =  6*89 
Copper-gold       .     .     .     .    „     =   15-02 
Copper-lead ,,     =   23-47 
Copper-platinum    .     .     .    „     =   42 -84 
Copper-tin „     =   24*71 
Copper-silver  ....,,=  1*29 
Zinc-copper  .  .  .  .  „  =  0*34 
The  theoretic  proof  of  the  signification  of  Peltier's  phenomena 
demonstrates  the  production  of  a  cooling  at  the  point  of  contact 
when  the  current  circulates  in  the  same  direction  as  the  current 
produced  by  the  electromotive  force  of  that  point.  As  the  cool- 
ing takes  place  at  the  point  of  contact  (between  iron  and  copper, 
for  example)  when  the  current  passes  from  the  copper  to  the  iron, 
this  signifies  that  the  electromotive  force  of  the  point  tends  to 
produce  a  current  from  the  copper  to  the  iron.  In  contact,  then, 
the  iron  becomes  electropositive,  and  the  copper  electronegative. 
It  is,  moreover,  well  established  by  experiment  that,  when  several 
metals,  A,  B,  C,  &c,  are  soldered  together  so  as  to  form  a  ring, 
no  current  results  if  all  the  points  of  contact  have  the  same  tem- 
perature. The  electromotive  force  between  A  and  C  must  there- 
fore be  of  the  same  amount  as  the  sum  of  the  forces  between  A  and 
B  and  B  and  C.  By  the  application  of  these  two  propositionswe 
obtain,  from  the  preceding  determinations,  the  following  electro- 
motive series,  commencing  with  the  most  positive,  and  ending  with 
the  most  negative  of  the  metals  investigated.  The  numbers  give 
the  electromotive  force  of  each  metal  in  contact  with  copper. 
oc. 
1-42*,. 
Mean. 
Iron      .     .     .     * 
{ 
132-501 
133-40J 
127-06 
130-99 
Cadmium  .     .     . 
6-87 
6-89 
6-88 
Zinc      .     .     . 
— 
0-34 
0-34 
Copper      .     .     . 
o-oo 
0-00 
o-oo 
Silver    . 
— 
1-29 
1-29 
Gold     .     .     . 
14-50 
15-02 
14-76 
Lead     .     .     . 
2093 
23-47 
22-20 
Tin       ... 
— 
24-71 
24-71 
Aluminium    . 
30-77 
— 
30-77 
Platinum  .     . 
47-22 
42-84 
45-03 
Palladium 
96-23 
— 
96-23 
Bismuth    .     . 
783-1 
— 
783-10 
i 
T( 
)  be  continued.] 
