98  Researches  on  the  Electromotive  Force  in  the  Contact  of  Metals, 
to  the  sources  of  heat  existing  in  each  cylinder.  It  may  now 
easily  happen,  in  the  course  of  the  observations,  that  the  tem- 
perature of  the  sides  is  relatively  low  in  the  cylinder  in  which 
the  point  of  contact  commences  to  cool  at  the  moment  of  the 
reversal  of  the  current,  and  that  the  temperature  of  the  sides  of 
the  other  cylinder  is  relatively  high  at  the  same  moment ;  the 
deviation  of  the  index  will  then  be  much  less  than  in  the  former 
case.  It  is  consequently  impossible  to  measure  with  certainty 
by  a  single  observation  the  movement  of  the  index ;  this  mea- 
surement can  only  be  obtained  by  taking  the  mean  of  a  great 
number  of  observations. 
The  metals  investigated  were  in  the  form  of  wires  of  about  1 
millim.  diameter,  except  those  of  bismuth,  tin,  and  lead,  which 
were  thicker.  The  copper  used  had  been  precipitated  by  the 
galvanic  method ;  and  the  metals  bismuth,  tin,  lead,  gold,  zinc, 
and  cadmium  had  been  chemically  purified  from  foreign  elements. 
The  silver  likewise  could  be  regarded  as  pure;  for  it  con- 
tained only  O'Ol  per  cent,  of  foreign  matter.  The  iron  con- 
tained O022  per  cent,  of  carbon,  0-006  of  silicium,  0-028  of 
phosphorus,  and  a  slight  trace  of  manganese,  but  was  free  from 
sulphur*.  In  each  combination,  copper  constituted  one  of  the 
wires — with  the  exception  of  the  pair  containing  palladium 
(which  was  soldered  to  a  platinum  wire),  and  that  containing 
zinc  (which  was  soldered  to  a  silver  wire).  All  the  solderings 
were  made  with  tin ;  the  aluminium  wire,  however,  had  to  be 
covered  with  a  layer  of  copper,  galvanically  deposited,  before  the 
soldering  could  take  place. 
The  intensity  of  the  current  was  regulated  by  means  of  a 
rheostat,  and  measured  by  a  tangent- compass.  The  circuit  was 
furnished  with  the  commutators  required  for  the  reversal  of  the 
current.  Before  the  commencement  of  a  series  of  observations, 
the  current  circulated  in  the  wires  during  one  or  several  hours, 
in  order  that  the  apparatus  might  have  time  to  acquire  equili- 
brium of  temperature. 
I  pass  now  to  the  observations  properly  so  called. 
*  I  owe  the  purification  of  these  metals  to  the  kindness  of  Professor 
Ekman  and  MM.  Cleve  and  Yfimmerstedt.     I  received  the  gold  and  silver 
from  the  royal  mint,  through  M.  Akerrnan,  the  Director0in  Chief  of  that 
establishment,  and  the  iron  through  Assistant  Professor  Akerman.  I  had 
obtained  the  palladium  from  England,  by  the  kindness  of  Mr.  Nassau 
Jocelyn,  Secretary  of  Legation  of  Her  Britannic  Majesty  at  the  court  of 
Stockholm. 
[To  be  continued.] 
