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  XIII. 
  Self 
  -Recording 
  Electrometer. 
  By 
  J. 
  Patterson, 
  M. 
  A. 
  t 
  

   Physicist 
  to 
  the 
  Meteorological 
  Service 
  of 
  Canada*. 
  

  

  [Plate 
  VI.] 
  

  

  Introduction, 
  

  

  BENNDORF 
  f 
  has 
  designed 
  an 
  electrometer 
  which 
  gives 
  a 
  

   continuous 
  record 
  by 
  mechanical 
  registration, 
  and 
  the 
  

   Cambridge 
  Scientific 
  Instrument 
  Co. 
  has 
  a 
  self-recording- 
  

   galvanometer 
  on 
  the 
  same 
  principle, 
  called 
  the 
  thread-recorder.. 
  

   In 
  the 
  Benndorf 
  instrument 
  the 
  apparatus 
  for 
  producing 
  the 
  

   registration 
  is 
  operated 
  by 
  an 
  electromagnet 
  worked 
  by 
  

   clockwork, 
  while 
  in 
  the 
  thread-recorder 
  it 
  is 
  all 
  done 
  by 
  

   clockwork. 
  It 
  occurred 
  to 
  the 
  author 
  that 
  the 
  recording 
  

   mechanism 
  of 
  the 
  thread-recorder 
  could 
  also 
  be 
  used 
  for 
  a 
  

   self-recording 
  electrometer 
  as 
  well 
  as 
  for 
  a 
  galvanometer. 
  

  

  In 
  these 
  instruments 
  a 
  boom 
  with 
  a 
  counterpoise 
  is 
  attached 
  

   to 
  the 
  axis 
  of 
  the 
  needle, 
  and 
  the 
  excursions 
  of 
  the 
  end 
  of 
  the 
  

   boom 
  are 
  registered 
  at 
  stated 
  intervals 
  by 
  a 
  bar 
  dropping 
  and 
  

   nipping 
  an 
  inked 
  thread 
  or 
  ribbon 
  between 
  the 
  boom 
  and 
  the 
  

   recording 
  paper, 
  thus 
  leaving 
  a 
  dot, 
  which 
  gives 
  the 
  deflexion 
  

   of 
  the 
  needle 
  at 
  the 
  moment 
  of 
  registration. 
  In 
  this 
  way 
  all 
  

   mechanical 
  friction 
  is 
  avoided. 
  

  

  Preliminary 
  Experiments. 
  

  

  Preliminary 
  experiments 
  were 
  made 
  by 
  roughly 
  con- 
  

   structing 
  models 
  of 
  the 
  electrometer 
  in 
  order 
  to 
  design 
  the 
  

   size 
  of 
  the 
  quadrants, 
  length 
  of 
  boom, 
  &c, 
  that 
  would 
  give 
  

   the 
  most 
  delicate 
  instrument, 
  and 
  at 
  the 
  same 
  time 
  be 
  as 
  

   compact 
  as 
  possible. 
  Throughout 
  this 
  paper, 
  " 
  The 
  sensi- 
  

   tiveness 
  of 
  the 
  instrument 
  " 
  refers 
  to 
  the 
  openness 
  of 
  scale. 
  

   An 
  adjustable 
  bifilar 
  suspension 
  of 
  silver 
  platinum 
  wire 
  was 
  

   used 
  in 
  all 
  the 
  preliminary 
  experiments. 
  The 
  quadrants 
  were 
  

   5 
  in. 
  in 
  diameter 
  and 
  \ 
  in. 
  between 
  the 
  faces, 
  and 
  a 
  needle 
  of 
  

   the 
  Dolezalek 
  type 
  4 
  \ 
  in. 
  in 
  diameter 
  was 
  made 
  of 
  silvered 
  

   mica. 
  The 
  needle 
  was 
  insulated 
  from 
  the 
  boom 
  and 
  was 
  

   damped 
  by 
  a 
  platinum 
  vane 
  dipping 
  in 
  a 
  jar 
  of 
  sulphuric 
  acid, 
  

   through 
  which 
  electrical 
  connexion 
  was 
  made 
  with 
  the 
  needle. 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  Read 
  before 
  the 
  Royal 
  Society 
  of 
  

   Canada, 
  May 
  25, 
  1913. 
  

  

  t 
  Akad. 
  Wiss. 
  Wien, 
  Sitzb. 
  d. 
  mathem.-naturw. 
  CI. 
  Bd. 
  cxi. 
  Abth. 
  I 
  la. 
  

   p. 
  487 
  (1902). 
  

  

  