﻿ir.8 
  Mr. 
  W. 
  Duddell 
  on 
  a 
  

  

  construction 
  for 
  carrying 
  out 
  the 
  experiment 
  at 
  0° 
  C. 
  There 
  

   should 
  be 
  no 
  difficulty 
  in 
  using 
  large 
  quantities 
  o£ 
  liquid 
  

   gases 
  as 
  a 
  means 
  o£ 
  obtaining 
  constant 
  high 
  pressures 
  provided 
  

   a 
  strong 
  enough 
  vessel 
  is 
  used. 
  

  

  ^,The 
  author 
  has 
  great 
  diffidence 
  in 
  expressing 
  any 
  opinion 
  

   as 
  to 
  the 
  value 
  of 
  these 
  experiments, 
  but 
  as 
  very 
  few 
  deter- 
  

   minations 
  of 
  the 
  Joule-Thomson 
  effect 
  have 
  been 
  published, 
  

   he 
  thinks 
  that 
  these 
  may 
  be 
  of 
  some 
  interest. 
  

  

  University 
  College, 
  

   Bloeinfontein, 
  O.K.O. 
  

  

  XVIII. 
  On 
  a 
  Bifilar 
  Vibration 
  Galvanometer. 
  

   By 
  W. 
  Duddell, 
  Fellow 
  of 
  the 
  Physical 
  Society 
  *. 
  

  

  IN 
  a 
  paper 
  read 
  before 
  this 
  Society 
  in 
  May 
  1907, 
  

   Mr. 
  Albert 
  Campbell 
  drew 
  attention 
  to 
  the 
  great 
  advan- 
  

   tages 
  of 
  vibration 
  galvanometers 
  in 
  the 
  measurement 
  of 
  

   mutual 
  inductances, 
  and 
  he 
  further 
  described 
  a 
  new 
  type 
  of 
  

   vibration 
  galvanometer 
  which 
  he 
  had 
  designed. 
  

  

  During 
  the 
  last 
  few 
  years 
  the 
  use 
  of 
  vibration 
  galvano- 
  

   meters 
  for 
  the 
  measurement 
  of 
  capacities, 
  self 
  and 
  mutual 
  

   inductions 
  has 
  greatly 
  extended, 
  and 
  in 
  the 
  near 
  future 
  they 
  

   may 
  be 
  expected 
  to 
  supersede 
  the 
  telephone 
  and 
  possibly 
  the 
  

   seeohmmeter, 
  for 
  these 
  purposes. 
  As 
  there 
  are 
  very 
  few 
  

   published 
  data 
  about 
  the 
  sensibility, 
  etc., 
  of 
  these 
  instruments 
  

   I 
  think 
  it 
  may 
  be 
  of 
  interest 
  to 
  describe 
  what 
  I 
  believe 
  to 
  be 
  

   a 
  new 
  type 
  and 
  a 
  series 
  of 
  tests 
  made 
  on 
  it. 
  

  

  Vibration 
  galvanometers 
  like 
  ordinary 
  galvanometers 
  may 
  

   be 
  broadly 
  divided 
  into 
  two 
  classes, 
  — 
  those 
  in 
  which 
  the 
  

   moving 
  part 
  consists 
  of 
  a 
  piece 
  of 
  iron 
  or 
  steel 
  and 
  the 
  

   current 
  to 
  be 
  measured 
  flows 
  round 
  fixed 
  coils 
  as 
  in 
  the 
  case 
  

   of 
  the 
  Thomson 
  galvanometer, 
  — 
  those 
  in 
  which 
  the 
  current 
  to 
  

   be 
  measured 
  flows 
  round 
  a 
  moving 
  coil 
  placed 
  in 
  a 
  fixed 
  

   magnetic 
  field 
  on 
  the 
  siphon 
  recorder 
  principle. 
  

  

  The 
  vibration 
  galvanometers 
  of 
  Max 
  Wien 
  and 
  Rubens 
  

   belong 
  to 
  the 
  first 
  class, 
  while 
  Mr. 
  Campbell's 
  moving 
  coil 
  

   vibration 
  galvanometer 
  belongs 
  to 
  the 
  second, 
  and 
  so 
  does 
  

   the 
  new 
  bifilar 
  instrument 
  described 
  below. 
  

  

  Generally 
  speaking, 
  when 
  one 
  requires 
  to 
  build 
  a 
  sensitive 
  

   instrument 
  having 
  a 
  short 
  periodic 
  time 
  it 
  is 
  necessary 
  to 
  

   reduce 
  as 
  far 
  as 
  possible 
  the 
  mass 
  of 
  the 
  moving 
  parts 
  in 
  

   order 
  to 
  combine 
  high 
  sensibility 
  with 
  short 
  period. 
  

  

  Further, 
  in 
  the 
  case 
  of 
  a 
  vibration 
  galvanometer, 
  it 
  is 
  also 
  

   necessary 
  to 
  keep 
  the 
  damping 
  forces 
  as 
  small 
  as 
  possible, 
  as 
  

  

  * 
  Communicated 
  by 
  the 
  Physical 
  Society 
  : 
  read 
  May 
  14, 
  1909. 
  

  

  