﻿370 
  Mr. 
  N. 
  E. 
  Gilbert 
  : 
  Experiments 
  upon 
  the 
  

  

  the 
  position 
  of 
  the 
  magnetic 
  pole 
  being 
  taken 
  from 
  the 
  same 
  

   article. 
  The 
  average 
  of 
  the 
  values 
  of 
  the 
  constant 
  C 
  derived 
  

   from 
  the 
  two 
  components 
  of 
  intensity 
  are 
  

  

  = 
  F 
  A 
  /cosX 
  = 
  '316, 
  2C 
  = 
  F 
  r 
  /sinA 
  = 
  -614; 
  

  

  and 
  these 
  agree 
  as 
  well 
  as 
  could 
  be 
  expected 
  in 
  view 
  of 
  the 
  

   irregularity 
  in 
  distribution 
  of 
  the 
  magnetic 
  elements 
  owing, 
  

   possibly, 
  to 
  unsymmetrical 
  permeability 
  and 
  conductivity 
  in 
  

   the 
  interior 
  and 
  particularly 
  to 
  local 
  causes 
  of 
  disturbance. 
  

   From 
  the 
  two 
  series 
  of 
  determinations 
  we 
  obtain 
  a 
  mean 
  

   value 
  C 
  = 
  *311. 
  Substituting 
  this 
  in 
  equation 
  (3) 
  with 
  

   T 
  = 
  86,400 
  sec. 
  and 
  A= 
  6336.10 
  5 
  cm. 
  we 
  have 
  K/p 
  = 
  1276.10- 
  17 
  

   (log= 
  6-10585-20). 
  

  

  It 
  now 
  remains 
  to 
  determine 
  by 
  experiment 
  whether 
  such 
  

   a 
  value 
  of 
  K 
  exists 
  as 
  shall 
  give 
  to 
  p 
  a 
  reasonable 
  value. 
  

  

  The 
  galvanometer 
  used 
  for 
  this 
  test 
  was 
  one 
  which 
  could 
  

   be 
  made 
  extremely 
  sensitive, 
  more 
  sensitive, 
  in 
  fact, 
  than 
  it 
  

   was 
  possible 
  to 
  use 
  in 
  Baltimore. 
  The 
  laboratory 
  has 
  trolley- 
  

   lines 
  on 
  two 
  sides, 
  and 
  a 
  railway 
  tunnel, 
  in 
  which 
  heavy 
  

   electric 
  locomotives 
  are 
  used, 
  passes 
  nearly 
  underneath. 
  As 
  

   a 
  result, 
  there 
  were 
  only 
  one 
  hundred 
  minutes 
  daily, 
  divided 
  

   into 
  three 
  periods 
  between 
  1.30 
  and 
  4 
  A.M., 
  when 
  the 
  instru- 
  

   ment 
  could 
  be 
  expected 
  to 
  be 
  usable, 
  and 
  occasionally 
  entire 
  

   nights 
  passed 
  without 
  the 
  possibility 
  of 
  obtaining 
  any 
  satis- 
  

   factory 
  readings. 
  Owing 
  to 
  this 
  cause 
  the 
  progress 
  of 
  the 
  

   work 
  has 
  been 
  slow 
  and 
  the 
  results 
  at 
  best 
  are 
  unsatisfactory. 
  

  

  The 
  magnetic 
  system 
  of 
  the 
  galvanometer 
  consisted 
  of 
  two 
  

   sets 
  of 
  magnets, 
  each 
  containing 
  three 
  small 
  magnets 
  about 
  

   one 
  eighth 
  of 
  an 
  inch 
  long, 
  mounted 
  on 
  a 
  tine 
  glass 
  thread 
  

   at 
  a 
  distance 
  apart 
  of 
  about 
  1 
  inch. 
  Midway 
  between 
  the 
  

   two 
  sets 
  of 
  magnets 
  was 
  placed 
  a 
  very 
  small 
  mirror. 
  The 
  

   inertia 
  of 
  the 
  whole 
  system 
  was 
  reduced 
  to 
  a 
  minimum. 
  

   The 
  suspension 
  was 
  a 
  quartz 
  fibre. 
  Frequent 
  attempts 
  were 
  

   made, 
  by 
  testing 
  the 
  sensibility 
  in 
  both 
  directions 
  on 
  the 
  

   scale, 
  to 
  determine 
  whether 
  there 
  was 
  any 
  appreciable 
  torsion 
  

   in 
  the 
  fibre, 
  but 
  none 
  was 
  detected 
  which 
  was 
  comparable 
  

   with 
  outside 
  irregularities, 
  though 
  the 
  system 
  sometimes 
  

   turned 
  through 
  several 
  turns 
  while 
  being 
  made 
  astatic. 
  A 
  

   magnetic 
  shield 
  consisting 
  of 
  three 
  concentric 
  cylinders 
  of 
  

   soft 
  iron 
  was 
  used 
  during 
  a 
  part 
  of 
  the 
  time, 
  but 
  even 
  with 
  

   this 
  the 
  galvanometer 
  could 
  be 
  used 
  only 
  during 
  the 
  three 
  

   quiet 
  periods. 
  It 
  was 
  found 
  advisable 
  to 
  demagnetize 
  the 
  

   shield 
  occasionally 
  either 
  by 
  heating 
  to 
  a 
  red 
  heat 
  or 
  by 
  

   placing 
  around 
  it 
  a 
  coil 
  carrying 
  an 
  alternating 
  current, 
  and 
  

   then 
  slowly 
  reducing 
  the 
  strength 
  of 
  the 
  current. 
  By 
  

   " 
  sensibility 
  " 
  of 
  the 
  galvanometer 
  is 
  meant 
  the 
  current 
  

  

  