﻿Self 
  -Re 
  cording 
  Electrometer. 
  

  

  203 
  

  

  The 
  method 
  of 
  attaching 
  the 
  boom 
  is 
  shown 
  diagram- 
  

   mat 
  ically 
  in 
  fig. 
  1. 
  The 
  rod 
  B 
  has 
  a 
  hook 
  on 
  each 
  end 
  to 
  

  

  Fig. 
  1. 
  

  

  St:rru-p 
  pu 
  oaxt 
  toslee\ 
  

  

  ^Quartz 
  tube 
  

  

  take 
  the 
  suspension 
  and 
  the 
  needle 
  respectively. 
  This 
  rod 
  

   is 
  insulated 
  by 
  the 
  quartz 
  tube 
  to 
  which 
  are 
  attached 
  the 
  

   sleeves 
  to 
  support 
  the 
  pointer 
  and 
  its 
  counterpoise. 
  In 
  order 
  

   to 
  adjust 
  the 
  needle 
  to 
  any 
  position 
  with 
  reference 
  to 
  the 
  

   pointer 
  or 
  boom, 
  the 
  sleeve 
  X 
  can 
  turn 
  on 
  the 
  sleeve 
  Z 
  and 
  

   is 
  clamped 
  in 
  position 
  by 
  the 
  screw 
  Y. 
  The 
  counterpoise 
  is 
  

   just 
  a 
  little 
  more 
  than 
  sufficient 
  to 
  balance 
  the 
  boom, 
  but 
  

   is 
  prevented 
  from 
  falling 
  below 
  the 
  horizontal 
  position 
  by 
  a 
  

   stop. 
  This 
  arrangement 
  permits 
  the 
  end 
  of 
  the 
  boom 
  to 
  

   be 
  depressed 
  without 
  disturbing 
  the 
  needle 
  or 
  bending 
  the 
  

   suspension. 
  

  

  The 
  weight 
  of 
  the 
  different 
  parts 
  in 
  grammes 
  is: 
  — 
  

  

  Weight. 
  

   One 
  vane 
  0*61 
  g. 
  

  

  ,, 
  „ 
  0-62 
  g. 
  

  

  Boom, 
  counterpoise, 
  needle, 
  rod, 
  &c 
  8'23 
  g. 
  

  

  Damping 
  vane 
  057 
  g. 
  

  

  Total 
  10-03 
  

  

  This 
  shows 
  then 
  that 
  the 
  addition 
  of 
  the 
  second 
  vane 
  only 
  

   adds 
  6 
  per 
  cent, 
  to 
  the 
  weight, 
  and 
  permits 
  as 
  fine 
  a 
  sus- 
  

   pension 
  to 
  be 
  used 
  for 
  the 
  two 
  vanes 
  as 
  for 
  one. 
  

  

  Two 
  views 
  of 
  the 
  completed 
  instrument 
  removed 
  from 
  its 
  

   case 
  are 
  shown 
  in 
  Plate 
  VI. 
  figs. 
  2 
  and 
  3. 
  

  

  The 
  quadrants 
  are 
  large 
  enough 
  to 
  permit 
  the 
  use 
  of 
  41 
  in. 
  

   vanes, 
  and 
  the 
  faces 
  of 
  the 
  plates 
  are 
  ^ 
  in. 
  apart*. 
  The 
  

  

  * 
  The 
  faces 
  of 
  the 
  plates 
  were 
  at 
  first 
  only 
  -, 
  3 
  8 
  in. 
  apart, 
  but 
  it 
  was 
  found 
  

   that 
  when 
  the 
  potential 
  on 
  the 
  needle 
  exceeded 
  200 
  volts 
  the 
  attraction 
  

   between 
  the 
  plates 
  and 
  the 
  vanes 
  of 
  the 
  needle 
  was 
  sufficient 
  to 
  cause 
  the 
  

   vanes 
  to 
  touch 
  the 
  plates 
  and 
  discharge, 
  owing 
  to 
  the 
  impossibility 
  of 
  

   adjusting 
  them 
  exactly 
  parallel 
  to 
  the 
  faces 
  of 
  the 
  plates. 
  The 
  plates 
  

   were 
  then 
  put 
  \ 
  in. 
  apart, 
  and 
  the 
  trouble 
  ceased. 
  

  

  