330         Dr.  Gundry  on  the  Asymmetrical  Action  of  an 
so-called  u  Electrolytic  Coherer."  This  instrument  was  in- 
troduced by  Fessenden*  and  S  chid  milch  t,  the  latter  of 
whom  made  the  first  penetrating  investigation  in  the  subject. 
Schlomilch.  as  is  well  known,  found  that  the  current  through 
an  electrolytic  cell,  in  wdiich  a  very  fine  point  of  platinum 
formed  the  anode,  and  to  which  an  E.M.F.  of  several  volts 
was  laid,  was  greatly  increased  by  excitation  with  electric 
waves.  He  found  a  negative  result  when  the  point  was  a 
cathode. 
The  explanation  of  Fessenden,  that  this  resulted  from  a 
warming  of  the  electrolyte  in  the  immediate  neighbourhood 
of  the  small  electrode,  was  proved  untenable.  Later  experi- 
ments (of  Rothmund  and  Lessing)  show  a  coherer  and  not 
an  anticoherer  effect,  when  the  electrolyte  (e.  g.  phosphoric 
acid  and  hypophosphorous  acid  at  higher  temperatures)  has 
a  negative  resistance  temperature  coefficient.  The  work  of 
Reich  J,  in  which  he  found  a  difference  when  sending  a  non- 
oscillating  discharge  of  a  Leyden-jar  through  the  cell  ac- 
cording to  the  direction  of  the  discharge,  led  him  to  explain 
the  phenomenon  as  a  depolarization  effect. 
A  great  addition  to  the  knowledge  of  the  facts  was  made 
by  Rothmund  and  Lessing  §.  In  the  first  place,  they  showed 
that  the  coherer  action  was  even  relatively  more  pronounced 
when  the  applied  E.M.F.  was  under  that  required  for  decom- 
position, and  that  under  these  circumstances  the  very  small 
polarization  current  was  increased  wrhen  the  point  was  a 
cathode  as  well  as  when  it  was  an  anode.  The  effect  of  the 
waves  was,  however,  much  greater  for  an  anodically  pola- 
rized point  than  for  a  cathodically  polarized  one.  The 
magnitude  of  the  effect  was  found  to  depend  in  very  great 
measure  on  the  sign  and  magnitude  of  the  direct-current 
polarization.  It  was  also  shown  that  the  E.M.F.  of  electric 
batteries,  in  which  a  small  point,  made  of  different  metals, 
formed  one  of  the  electrodes,  was  altered  by  the  action  of 
electric  waves. 
On  the  theoretical  side  there  is,  so  far  as  I  know,  no 
satisfactory  explanation.  The  idea  of  the  depolarization  set 
forth  by  Rothmund  and  Lessing,  by  which  one  phase  of  the 
alternating  current  passes  easily  from  electrolyte  to  electrode 
owing  to  oxidation,  the  other  with  difficulty,  based  on  a 
comparison  with  the  aluminium  rectifier,  appears  to  help  but 
little  to  a  clear  understanding  of  the  question.     A  satisfactory 
*  Fessenden,  Elektrotech.  Zeitsch.  xxiv.  pp.  586  &  1015  (1903). 
t  Schlomilch,  ibid.  xxiv.  p.  959  (1903). 
X  M.  Reich,  Phys.  Zeilschr.  v.  p.  338  (1904). 
§  Rothmund  and  Lessing,  Drude  Ami.  xv.  p.  193  (1904). 
