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LIX.  The  Construction  and  Use  of  Oscillation  Valves  for 
Rectifying  High- Frequency  Electric  Currents.  By  J.  A. 
Fleming,  M.A.,  D.Sc,  F.E.S.,  Professor  of  Electrical 
Engineering  in  University  College,  London*. 
ATTENTION  was  directed  by  the  author  in  1890  to  the 
fact  that  i£  two  carbon  filaments  are  sealed  into  a 
single  vacuous  glass  bulb  so  as  to  make  an  incandescent  lamp 
with  two  separate  carbon  loops,  the  resistance  between  these 
filaments,  though  infinite  when  the  carbon  is  cold,  becomes 
quite  small  as  soon  as  the  loops  are  made  incandescent  f. 
Moreover,  i£  a  metal  plate  is  sealed  into  an  incandescent 
lamp  it  was  shown  that  the  space  between  the  metal  plate 
and  the  incandescent  carbon  filament  possesses  a  unilateral 
conductivity,  negative  electricity  being  able  to  pass  freely 
from  the  hot  carbon  to  the  plate,  but  not  in  the  opposite 
direction  %.  More  recently  the  author  discovered  that  such 
an  arrangement  may  be  used  as  a  valve  to  permit  the  passage 
of  one  constituent  current  only  of  a  high-frequency  current 
or  to  rectify  an  electric  oscillation  §.  The  reason  for  this 
action  is  now  recognized  to  be  the  copious  emission  of  negative 
ions  or  electrons  from  the  incandescent  carbon.  This  opera- 
tion has  been  studied  quantitatively  by  the  present  writer  and 
many  other  observers. 
For  the  purpose  of  rectifying  electrical  oscillations  and 
thus  be  able  to  detect  them  by  an  ordinary  galvanometer, 
these  oscillation  valves  are  now  made  as  follows  : — A  carbon- 
filament  glow-lamp  is  constructed,  the  carbon  loop  o^ 
which  is  upheld  in  the  centre  of  a  highly  exhausted  glass 
bulb  (see  fig.  1).  Around  the  loop  is  fixed  a  small  cylinder 
of  nickel,  C,  which  is  connected  to  a  platinum  wire  sealed 
through  the  side  of  the  bulb.  The  valve  is  used  as  follows: — 
The  carbon  loop  is  made  incandescent  by  a  suitable  battery 
of  secondary  cells,  a  sliding  rheostat  being  added  to  adjust 
the  voltage  on  the  terminals  of  the  lamp.  The  circuit  in 
which  oscillations  are  to  be  detected  is  joined  in  series  with 
a  dead-beat  mirror-galvanometer,  and  the  valve  connected 
with  the  circuit  by  wires  joined  respectively  to  the  terminal 
of  the  nickel  cylinder  and  the  negative  terminal  of  the  carbon 
*  Communicated  by  the  Physical  Society:  read  March  23,  1906. 
t  See  J.  A.  Fleming,  "  On  Electric  Discharge  between  Electrodes  at 
Different  Temperatures  in  Air  and  High  Vacua/'  Proc.  Hoy.  Soc.  Loud, 
vol.  xlvii.  p.  122  (1890) ;  also  "  Problems  on  the  Physics  of  an  Electric 
Lamp,"  Proc.  Royal  Institution,  vol.  xiii.  part  34,  p.  45  (1S90). 
\  See  J.  A.  Fleming,  "On  a  Further  Examination  of  the  Edison  Effect 
in  Glow-Lamps,"  Phil.  Mag.  July  1890. 
§  See  also  Proc.  Roy.  Soc.  Lond.  vol.  lxxiv.  p.  470,  190o,  "On  the 
Conversion  of  Electrical  Oscillations  into  Continuous  Currents  by  means 
of  a  Vacuum  Valve." 
