﻿llectric 
  Wind 
  from 
  a 
  Discharging 
  Point. 
  

  

  695 
  

  

  used 
  in 
  previous 
  experiments 
  to 
  measure 
  the 
  wind-pressure, 
  

   is 
  not 
  suitable 
  for 
  work 
  at 
  different 
  atmospheric 
  pressures, 
  

   since 
  it 
  requires 
  a 
  somewhat 
  cumbersome 
  mercury 
  trap 
  to 
  

   prevent 
  the 
  boiling 
  of 
  the 
  liquid 
  indicator 
  under 
  reduced 
  

   pressure. 
  For 
  the 
  final 
  experiments, 
  after 
  various 
  trials, 
  the 
  

   recently 
  described 
  Fry 
  micro 
  mano 
  meter 
  * 
  was 
  set 
  up. 
  

  

  This 
  gauge 
  consists 
  of 
  two 
  compartments 
  separated 
  by 
  a 
  

   diaphragm. 
  When 
  a 
  difference 
  of 
  pressure 
  is 
  put 
  on 
  between 
  

   the 
  compartments 
  a 
  movement 
  of 
  the 
  diaphragm 
  results, 
  and 
  

   is 
  shown 
  by 
  the 
  movement 
  of 
  a 
  spot 
  of 
  light 
  reflected 
  from 
  

   a 
  mirror 
  suspended 
  in 
  a 
  special 
  manner. 
  The 
  details 
  of 
  con- 
  

   struction 
  and 
  calibration 
  are 
  given 
  in 
  full 
  in 
  the 
  original 
  

  

  Fig. 
  1. 
  

  

  paper. 
  Gauges 
  of 
  this 
  type 
  have 
  been 
  constructed 
  to 
  indicate 
  

   a 
  pressure 
  of 
  *001 
  dyne 
  per 
  sq. 
  cm., 
  though 
  it 
  was 
  not 
  

   necessary 
  to 
  use 
  such 
  a 
  sensitive 
  form 
  in 
  the 
  present 
  work. 
  

   The 
  actual 
  pressures 
  measured 
  ranged 
  from 
  *06 
  to 
  1*2 
  dynes 
  

   per 
  sq. 
  cm. 
  . 
  

  

  The 
  discharge 
  -tube 
  D 
  (fig. 
  1) 
  was 
  of 
  glass 
  and 
  was 
  closed 
  

   top 
  and 
  bottom 
  with 
  insulating 
  stoppers. 
  The 
  compartments 
  

   above 
  and 
  below 
  the 
  plane 
  were 
  connected 
  by 
  glass 
  tubes 
  to 
  

   the 
  two 
  sides 
  of 
  the 
  gauge. 
  Drying-tubes 
  and 
  a 
  manometer 
  M 
  

  

  * 
  Phil. 
  Mag. 
  April 
  1913. 
  

   3 
  A 
  2 
  

  

  