﻿Problem 
  of 
  the 
  Amagnetic 
  Mariner's 
  Compass. 
  731 
  

  

  play 
  in 
  the 
  upper 
  (or, 
  in 
  the 
  cases 
  of 
  suspensions, 
  in 
  the 
  

   lower) 
  bearing, 
  and 
  therefore 
  a 
  tilting 
  of 
  the 
  horizontal 
  axis 
  

   of 
  the 
  gyrostat, 
  so 
  soon 
  as 
  forces 
  arise, 
  which 
  turn 
  the 
  upper 
  

   (or, 
  in 
  the 
  case 
  of 
  suspensions, 
  the 
  lower) 
  end 
  of 
  the 
  vertical 
  

   axis 
  ever 
  so 
  little 
  in 
  its 
  bearing, 
  being 
  unavoidable. 
  

  

  The 
  smallest 
  forced 
  nutation 
  of 
  a 
  gyrostat's 
  axis, 
  namely^ 
  

   is 
  enough, 
  as 
  Fessel 
  and 
  Pliicker 
  showed 
  with 
  their 
  so-called 
  

   precession 
  apparatus*, 
  and 
  as 
  one 
  could 
  demonstrate 
  with 
  

   Bohnenberger's 
  machine 
  t, 
  to 
  excite 
  a 
  force-component, 
  

   which 
  constrains 
  the 
  whole 
  system 
  to 
  rotate 
  round 
  a 
  third 
  

   axis, 
  perpendicular 
  to 
  both 
  that 
  of 
  the 
  gyrostat 
  and 
  that 
  

   of 
  nutation. 
  This 
  last 
  axis, 
  in 
  the 
  case 
  of 
  a 
  ship's 
  gyrostat^ 
  

   is 
  unfortunately 
  exactly 
  the 
  vertical 
  axis, 
  round 
  which 
  it 
  

   should 
  turn 
  for 
  indicating 
  the 
  course. 
  Therefore, 
  every 
  

   acceleration 
  of 
  the 
  ship^s 
  motion 
  — 
  whether 
  it 
  be 
  rectilinear 
  

   or 
  curvilinear 
  — 
  acts 
  so 
  as 
  to 
  deflect 
  the 
  gyrostat 
  ; 
  and 
  we 
  

   are 
  not, 
  in 
  general, 
  in 
  a 
  position 
  to 
  separate 
  this 
  deflecting 
  

   eft'ect 
  from 
  the 
  visible 
  deviations, 
  by 
  which 
  a 
  change 
  in 
  the 
  

   ship''s 
  course 
  should 
  be 
  revealed. 
  The 
  greater 
  the 
  gyrostatic 
  

   moment 
  of 
  inertia, 
  the 
  smaller 
  will 
  be 
  the 
  influence 
  of 
  the 
  

   disturbances, 
  but 
  the 
  greater 
  will 
  be 
  the 
  time-period 
  of 
  the 
  

   oscillation 
  of 
  the 
  amagnetic 
  compass, 
  — 
  far 
  above 
  the 
  limit 
  

   permitting 
  one 
  to 
  distinguish 
  at 
  every 
  instant 
  between 
  oscil- 
  

   lations 
  of 
  the 
  compass-card 
  and 
  rotations 
  of 
  the 
  ship. 
  

  

  So 
  some 
  years 
  ago 
  (1904) 
  I 
  entered 
  upon 
  a 
  completely 
  new 
  

   mode 
  of 
  treating 
  the 
  problem, 
  after 
  it 
  appeared 
  to 
  me, 
  that 
  

   above 
  everything 
  the 
  instrument 
  itself 
  should 
  indicate 
  con- 
  

   tinually, 
  whether 
  its 
  action 
  is 
  to 
  be 
  depended 
  upon, 
  — 
  and 
  this 
  

   in 
  the 
  simplest 
  manner, 
  so 
  that 
  it 
  should 
  indicate 
  either 
  with 
  

   unfailing 
  correctness 
  or 
  not 
  indicate 
  at 
  all 
  ; 
  consequently 
  

   the 
  fact 
  that 
  it 
  is 
  in 
  operation 
  might 
  at 
  the 
  same 
  time 
  be 
  a 
  

   guarantee, 
  that 
  it 
  operates 
  correctly, 
  and 
  that, 
  further, 
  it 
  is 
  

   to 
  be 
  recommended, 
  that 
  the 
  would-be 
  vertical 
  axis 
  should, 
  if 
  

   feasible, 
  be 
  altogether 
  done 
  away 
  with. 
  

  

  This 
  consideration 
  led 
  me 
  to 
  a 
  principle 
  of 
  arrangement, 
  

   which 
  up 
  till 
  now 
  had 
  been 
  most 
  carefully 
  avoided 
  : 
  a 
  dis- 
  

   turbance 
  of 
  the 
  position, 
  but 
  one, 
  which 
  is 
  periodic, 
  with 
  a 
  

   fresh 
  adjustment 
  always 
  following 
  it. 
  The 
  playing 
  forces 
  

   arising 
  from 
  a 
  complexity 
  of 
  rotations, 
  which 
  must 
  be 
  given 
  

   a 
  priori, 
  the 
  nature 
  of 
  the 
  new 
  total 
  configuration 
  is 
  charac- 
  

   terized 
  as 
  of 
  a 
  higher 
  order, 
  of 
  which 
  the 
  gyrostat 
  constitutes 
  

   but 
  an 
  organic 
  member 
  : 
  in 
  distinction 
  from 
  previous 
  

  

  * 
  Fessel's 
  precession 
  apparatus, 
  described 
  by 
  Pliicker 
  and 
  by 
  Poggen- 
  

   dorff, 
  see 
  Annalen 
  der 
  F/iys. 
  u, 
  Chem. 
  vol. 
  xc, 
  1853. 
  

  

  t 
  See 
  my 
  communication, 
  " 
  Simple 
  Diagram 
  connecting 
  the 
  various 
  

   motions 
  in 
  the 
  so-called 
  Bohnenberger's 
  machine," 
  Phil. 
  Mag. 
  ser. 
  6,. 
  

  

  3C2 
  

  

  