﻿758 
  Mr. 
  W. 
  A. 
  Jenkins 
  : 
  New 
  Method 
  of 
  Determining 
  the 
  

  

  The 
  mirror 
  was 
  fastened 
  to 
  the 
  aluminium 
  holder 
  directly 
  

   under 
  the 
  point 
  of 
  suspension 
  and 
  perpendicular 
  to 
  the 
  

   length 
  of 
  the 
  magnet. 
  Some 
  little 
  trouble 
  was 
  experienced 
  

   in 
  getting 
  this 
  latter 
  condition 
  accurately 
  fulfilled, 
  but 
  its 
  

   necessity 
  is 
  obvious. 
  A 
  silvered 
  piece 
  of 
  microscope 
  cover- 
  

   glass 
  served 
  as 
  a 
  mirror. 
  

  

  Owing 
  to 
  the 
  light 
  weight 
  which 
  the 
  fibre 
  has 
  to 
  support 
  

   an 
  extremely 
  fine 
  one 
  can 
  be 
  used. 
  This 
  is 
  of 
  great 
  ad- 
  

   vantage, 
  for 
  it 
  was 
  found 
  that 
  unless 
  the 
  finest 
  obtainable 
  

   fibre 
  was 
  used 
  the 
  vibrations 
  died 
  out 
  rather 
  too 
  quickly 
  to 
  

   allow 
  of 
  accurate 
  observations 
  of 
  the 
  time 
  of 
  swing 
  being 
  

   made. 
  For 
  this 
  same 
  reason 
  the 
  area 
  of 
  the 
  surface 
  of 
  the 
  

   mirror 
  was 
  made 
  as 
  small 
  as 
  possible. 
  

  

  In 
  order 
  to 
  rid 
  the 
  fibre 
  of 
  torsion, 
  the 
  suspension 
  mechanism 
  

   was 
  placed 
  parallel 
  to 
  the 
  earth's 
  field, 
  and 
  a 
  piece 
  of 
  brass, 
  

   similar 
  in 
  weight 
  to 
  the 
  magnet, 
  inserted 
  in 
  the 
  holder. 
  It 
  

   was 
  now 
  allowed 
  to 
  come 
  to 
  rest, 
  and 
  then 
  the 
  suspension- 
  

   head 
  was 
  turned 
  until 
  its 
  zero 
  position 
  was 
  in 
  a 
  direction 
  

   parallel 
  to 
  the 
  earth's 
  field. 
  On 
  placing 
  the 
  magnet 
  in 
  the 
  

   holder 
  no 
  further 
  twisting 
  took 
  place, 
  and 
  very 
  little 
  torsion 
  

   was 
  left 
  in 
  the 
  fibre. 
  When 
  the 
  suspension 
  apparatus 
  was 
  

   in 
  the 
  solenoid, 
  a 
  strip 
  of 
  brass 
  was 
  screwed 
  into 
  the 
  end 
  of 
  

   the 
  tube 
  in 
  order 
  to 
  support 
  the 
  brass 
  rod 
  and 
  prevent 
  

   sagging. 
  

  

  Optical 
  Arrangement 
  for 
  timing 
  the 
  Oscillations. 
  

  

  The 
  period 
  of 
  vibration 
  was 
  found 
  by 
  means 
  of 
  the 
  mirror 
  

   attached 
  to 
  the 
  magnet. 
  Light 
  from 
  a 
  Nernst 
  lamp 
  was 
  

   reflected 
  by 
  a 
  piece 
  of 
  plane 
  glass, 
  so 
  that 
  it 
  passed 
  down 
  

   the 
  solenoid 
  tube 
  and 
  on 
  to 
  the 
  mirror. 
  A 
  telescope 
  was 
  

   then 
  focussed 
  on 
  the 
  image 
  of 
  the 
  filament 
  of 
  the 
  Nernst 
  

   lamp 
  formed 
  by 
  the 
  mirror. 
  When 
  the 
  magnet 
  oscillates, 
  

   the 
  image 
  of 
  the 
  filament 
  crosses 
  the 
  field 
  of 
  view 
  of 
  the 
  

   telescope, 
  and 
  the 
  exact 
  moment 
  of 
  the 
  image 
  of 
  the 
  filament 
  

   crossing 
  the 
  cross-wire 
  of 
  the 
  telescope 
  is 
  easily 
  noticed. 
  

   The 
  eye-and-ear 
  method 
  was 
  used 
  in 
  the 
  actual 
  experiment. 
  

   An 
  ordinary 
  lamp 
  and 
  clear 
  glass 
  scale 
  were 
  used 
  in 
  the 
  

   preliminary 
  observations, 
  but 
  it 
  was 
  difficult 
  to 
  pick 
  out 
  any 
  

   particular 
  scale-division 
  when 
  timing 
  the 
  oscillation, 
  and 
  the 
  

   Nernst 
  filament 
  was 
  found 
  much 
  more 
  satisfactory. 
  When 
  

   the 
  magnet 
  is 
  reversed, 
  the 
  image 
  of 
  the 
  filament 
  is 
  still 
  

   seen 
  in 
  the 
  telescope, 
  reflected 
  from 
  the 
  back 
  of 
  the 
  same 
  

   mirror. 
  

  

  