﻿[ 
  277 
  ] 
  

  

  XXXI. 
  On 
  Electric 
  Equilibrium 
  between 
  Uranium 
  and 
  an 
  

   Insulated 
  Metal 
  in 
  its 
  Neighbourhood. 
  By 
  Lord 
  Kelvin, 
  

   G.C.V.O., 
  J. 
  Oarruthers 
  Bbattie, 
  D.Sc, 
  F.R.S.E., 
  

   and 
  M. 
  Smoluchowski 
  de 
  Smolan, 
  Ph.D.* 
  

  

  THE 
  wonderful 
  fact 
  that 
  uranium 
  held 
  in 
  the 
  neighbourhood 
  

   of 
  an 
  electrified 
  body 
  diselectrifies 
  it 
  was 
  first 
  discovered 
  

   by 
  H. 
  Becquerel. 
  Through 
  the 
  kindness 
  of 
  M. 
  Moissan 
  we 
  

   have 
  had 
  a 
  disk 
  of 
  this 
  metal, 
  about 
  5 
  centim. 
  in 
  diameter 
  and 
  

   •J 
  centim. 
  in 
  thickness, 
  placed 
  at 
  our 
  disposal. 
  

  

  We 
  made 
  a 
  few 
  preliminary 
  observations 
  on 
  its 
  diselec- 
  

   trifying 
  property. 
  We 
  observed 
  first 
  the 
  rate 
  of 
  discharge 
  

   when 
  a 
  body 
  was 
  charged 
  to 
  different 
  potentials. 
  We 
  found 
  

   that 
  the 
  quantity 
  lost 
  per 
  half-minute 
  was 
  very 
  far 
  from 
  

   increasing 
  in 
  simple 
  proportion 
  to 
  the 
  voltage, 
  from 
  5 
  volts 
  

   up 
  to 
  2100 
  volts; 
  the 
  electrified 
  body 
  being 
  at 
  a 
  distance 
  of 
  

   about 
  2 
  centim. 
  from 
  the 
  uranium 
  disk. 
  [Added 
  March 
  9. 
  — 
  

   We 
  hare 
  to-day 
  seen 
  Prof. 
  Becquerers 
  paper 
  in 
  Comptes 
  

   Rendus 
  for 
  March 
  1. 
  It 
  gives 
  us 
  great 
  pleasure 
  to 
  find 
  that 
  

   the 
  results 
  we 
  have 
  obtained 
  on 
  discharge 
  by 
  uranium 
  at 
  

   different 
  voltages 
  have 
  been 
  obtained 
  in 
  another 
  way 
  bv 
  the 
  

   discoverer 
  of 
  the 
  effect. 
  A 
  very 
  interesting 
  account 
  will 
  be 
  

   found 
  in 
  the 
  paper 
  above 
  cited, 
  which 
  was 
  read 
  to 
  the 
  French 
  

   Academy 
  of 
  Sciences 
  on 
  the 
  same 
  evening, 
  curiously 
  enough, 
  

   as 
  ours 
  was 
  read 
  before 
  the 
  Royal 
  Society 
  of 
  Edinburgh.] 
  

  

  These 
  first 
  experiments 
  were 
  made 
  with 
  no 
  screen 
  placed 
  

   between 
  the 
  uranium 
  and 
  the 
  charged 
  body. 
  We 
  afterwards 
  

   found 
  that 
  there 
  was 
  also 
  a 
  discharging 
  effect, 
  though 
  much 
  

   slower, 
  when 
  the 
  uranium 
  was 
  wrapped 
  in 
  tinfoil. 
  The 
  effect 
  

   was 
  still 
  observable 
  when 
  an 
  aluminium 
  screen 
  was 
  placed 
  

   between 
  the 
  uranium, 
  wrapped 
  in 
  tinfoil, 
  and 
  the 
  cbarp-ed 
  

   body. 
  

  

  To 
  make 
  experiments 
  on 
  the 
  electric 
  equilibrium 
  between 
  

   uranium 
  and 
  a 
  metal 
  in 
  its 
  neighbourhood, 
  we 
  connected 
  an 
  in- 
  

   sulated 
  horizontal 
  metal 
  disk 
  to 
  the 
  insulated 
  pair 
  of 
  quadrants 
  

   of 
  an 
  electrometer. 
  We 
  placed 
  the 
  uranium 
  opposite 
  this 
  

   disk 
  and 
  connected 
  it 
  and 
  the 
  other 
  pair 
  of 
  quadrants 
  of 
  the 
  

   electrometer 
  to 
  sheaths. 
  The 
  surface 
  of 
  the 
  uranium 
  was 
  

   parallel 
  to 
  that 
  of 
  the 
  insulated 
  metal 
  disk, 
  and 
  at 
  a 
  distance 
  

   of 
  about 
  1 
  centim. 
  from 
  it. 
  It 
  was 
  so 
  arranged 
  as 
  to 
  allow 
  

   of 
  its 
  easy 
  removal. 
  

  

  With 
  a 
  polished 
  aluminium 
  disk 
  as 
  the 
  insulated 
  metal 
  and 
  

   w 
  T 
  ith 
  a 
  similar 
  piece 
  of 
  aluminium 
  placed 
  opposite 
  it 
  in 
  place 
  

   of 
  the 
  uranium, 
  no 
  deviation 
  from 
  the 
  metallic 
  zero 
  was 
  found 
  

  

  * 
  Communicated 
  by 
  Lord 
  Kelvin 
  : 
  read 
  before 
  the 
  Roval 
  Society 
  of 
  

   Edinburgh, 
  March 
  1, 
  1897. 
  

  

  