﻿800 
  

  

  Mr. 
  H. 
  L. 
  P. 
  Jolly 
  on 
  the 
  

  

  measured, 
  the 
  disturbances 
  from 
  outside 
  are 
  to 
  be 
  contended 
  

   with. 
  Under 
  the 
  circumstances, 
  three 
  paths 
  seemed 
  open 
  to 
  

   bring 
  the 
  measurements 
  within 
  the 
  region 
  of 
  possibility. 
  

   The 
  galvanometer 
  could 
  be 
  made 
  aperiodic, 
  by 
  decreasing 
  the 
  

   controlling 
  force 
  on 
  the 
  magnet-system. 
  The 
  length 
  of 
  the 
  

   optical 
  path 
  used 
  to 
  read 
  the 
  deflexions 
  could 
  be 
  increased, 
  

   if 
  care 
  were 
  taken 
  with 
  the 
  optical 
  arrangements. 
  

  

  Finally, 
  it 
  seemed 
  worth 
  while 
  to 
  try 
  to 
  improve 
  on 
  the 
  

   means 
  of 
  obtaining 
  a 
  concentrated 
  supply 
  of 
  radiation 
  from 
  a 
  

   gas 
  in 
  a 
  discharge-tube. 
  All 
  of 
  these 
  improvements 
  were 
  

   tried, 
  and 
  as 
  a 
  result 
  of 
  pushing 
  the 
  sensitiveness 
  of 
  the 
  

   galvanometer 
  further, 
  some 
  comparatively 
  large 
  deflexions 
  

   were 
  obtained. 
  But 
  every 
  physicist 
  knows 
  the 
  futility 
  of 
  

   working 
  with 
  an 
  instrument 
  which 
  has 
  been 
  coaxed 
  into 
  

   ultra-sensitiveness. 
  

  

  A 
  description 
  of 
  some 
  of 
  the 
  observations 
  with 
  the 
  Broca 
  

   galvanometer 
  will 
  be 
  given 
  as 
  part 
  of 
  the 
  sequence 
  of 
  the 
  

   work, 
  but 
  no 
  real 
  scientific 
  value 
  is 
  claimed 
  for 
  them. 
  

  

  As 
  source 
  of 
  current 
  a 
  Ruhmkorff 
  coil 
  was 
  at 
  first 
  used, 
  

   and 
  later 
  a 
  transformer 
  which 
  took 
  the 
  lOO-volt 
  supply 
  

   directly. 
  

  

  Fig. 
  1 
  represents 
  the 
  forces 
  acting 
  on 
  the 
  magnet-system. 
  

  

  Fi-r. 
  l. 
  

  

  The 
  couple 
  due 
  to 
  the 
  earth's 
  field 
  is 
  represented 
  by 
  the 
  sine 
  

   curve, 
  and 
  the 
  torsional 
  couple 
  of 
  the 
  suspending 
  fibre 
  by 
  the 
  

   straight 
  line. 
  The 
  resultant 
  couple 
  is 
  given 
  by 
  the 
  vertical 
  

   height 
  of 
  the 
  shaded 
  area, 
  and 
  it 
  will 
  easily 
  be 
  seen 
  how 
  

   unstable 
  the 
  system 
  may 
  become 
  when 
  the 
  loop 
  is 
  made 
  

   narrower 
  so 
  as 
  to 
  increase 
  the 
  sensitiveness. 
  The 
  equilibrium 
  

   position 
  is 
  0, 
  but 
  if 
  the 
  system 
  should 
  be 
  driven 
  beyond 
  the 
  

  

  