﻿586 
  

  

  Staff- 
  Commander 
  E. 
  W. 
  Creak 
  on 
  the 
  

  

  [June 
  17, 
  

  

  This 
  vessel 
  was 
  built 
  at 
  Woolwich, 
  head 
  S. 
  16° 
  W., 
  and 
  fitted 
  out 
  at 
  

   Sheerness 
  ; 
  and 
  the 
  coefficients 
  obtained 
  in 
  her 
  at 
  two 
  positious 
  have 
  been 
  

   introduced 
  to 
  confirm 
  and 
  supplement 
  those 
  of 
  the 
  ' 
  Newcastle,' 
  espe- 
  

   cially 
  as 
  she 
  is 
  of 
  the 
  same 
  construction, 
  although 
  smaller, 
  and 
  has 
  

   wooden 
  masts. 
  

  

  The 
  notation 
  and 
  methods 
  of 
  computation 
  of 
  these 
  coefficients 
  are 
  

   those 
  given 
  in 
  the 
  Admiralty 
  Manual 
  of 
  the 
  Deviations 
  of 
  the 
  Compass. 
  

  

  The 
  standard 
  compasses 
  are 
  all 
  within 
  3 
  inches 
  of 
  12 
  feet 
  6 
  inches 
  

   above 
  the 
  upper 
  deck, 
  the 
  steering-compasses 
  3 
  feet 
  9 
  inches 
  above 
  that 
  

   deck, 
  and 
  6 
  feet 
  apart. 
  

  

  An 
  examination 
  of 
  the 
  values 
  given 
  in 
  the 
  Table 
  shows 
  that 
  about 
  8° 
  

   have 
  been 
  added 
  to 
  the 
  B 
  of 
  the 
  'Undaunted's' 
  standard, 
  but 
  the 
  C 
  

   remains 
  practically 
  unaltered. 
  This 
  is 
  evidently 
  the 
  effect 
  of 
  the 
  red 
  

   pole 
  of 
  the 
  mast 
  repelling 
  the 
  red 
  pole 
  of 
  the 
  compass 
  towards 
  the 
  bow, 
  

   and 
  thus 
  conspiring 
  with 
  the 
  other 
  iron 
  of 
  the 
  ship 
  to 
  produce 
  a 
  large 
  

   + 
  B. 
  Both 
  the 
  mast 
  and 
  compass 
  being 
  in 
  the 
  same 
  fore-and-aft 
  line, 
  

   the 
  C 
  cannot 
  be 
  altered, 
  and 
  depends 
  for 
  its 
  amount 
  and 
  sign 
  on 
  the 
  

   diagonal 
  riders 
  before 
  referred 
  to. 
  There 
  is 
  nothing 
  unusual 
  in 
  the 
  

   values 
  of 
  A, 
  D, 
  E, 
  except 
  that 
  the 
  'Undaunted's' 
  D 
  ranks 
  among 
  the 
  

   largest 
  observed 
  in 
  wooden 
  vessels. 
  

  

  The 
  A 
  (or 
  the 
  ratio 
  of 
  the 
  mean 
  horizontal 
  force 
  on 
  board 
  to 
  that 
  on 
  

   shore, 
  Earth 
  = 
  1*0) 
  is 
  at 
  all 
  the 
  compasses 
  a 
  fraction 
  above 
  unity. 
  This 
  

   probably 
  proceeds 
  from 
  the 
  fact, 
  already 
  recorded, 
  that 
  the 
  iron 
  in 
  these 
  

   ships 
  is 
  in 
  detached 
  masses 
  instead 
  of 
  its 
  direction 
  passing 
  continuously 
  

   through 
  the 
  compasses 
  like 
  iron 
  beams, 
  which 
  invariably 
  reduce 
  X 
  below 
  

   unity. 
  

  

  The 
  fx 
  (or 
  the 
  ratio 
  of 
  the 
  mean 
  vertical 
  force 
  on 
  board 
  to 
  that 
  on 
  

   shore, 
  Earth 
  =1*0) 
  in 
  the 
  ' 
  Challenger' 
  shows 
  how 
  the 
  red 
  poles 
  of 
  the 
  

   diagonal 
  riders 
  act 
  in 
  producing 
  an 
  upward 
  force 
  ; 
  but 
  had 
  the 
  riders 
  

   been 
  joined 
  at 
  the 
  keelson, 
  it 
  is 
  almost 
  certain 
  that 
  the 
  yu 
  would 
  have 
  

   been 
  nearer 
  unity 
  at 
  the 
  expense 
  of 
  X 
  — 
  a 
  more 
  desirable 
  result, 
  for 
  this 
  

   reason 
  : 
  experience 
  has 
  shown 
  that 
  X 
  may 
  be 
  reduced 
  moderately 
  below 
  

   unity 
  with 
  no 
  appreciable 
  effect 
  on 
  the 
  working 
  of 
  the 
  compasses, 
  whereas 
  

   H, 
  upon 
  which 
  the 
  heeling-error 
  so 
  much 
  depends, 
  should 
  in 
  wooden 
  ships 
  

   be 
  as 
  near 
  unity 
  as 
  possible, 
  heeling-error 
  being 
  troublesome 
  to 
  all 
  navi- 
  

   gators, 
  and 
  an 
  insidious 
  source 
  of 
  danger 
  to 
  the 
  inexperienced. 
  

  

  In 
  the 
  ' 
  Undaunted' 
  the 
  ji 
  at 
  all 
  compasses 
  is 
  evidently 
  much 
  reduced 
  

   by 
  the 
  vertical 
  component 
  of 
  the 
  force 
  produced 
  by 
  the 
  red 
  pole 
  of 
  the 
  

   iron 
  mast, 
  which 
  pole 
  is 
  very 
  strong 
  at 
  a 
  distance 
  of 
  16 
  feet, 
  and 
  at 
  an 
  

   angle 
  of 
  35° 
  from 
  the 
  vertical 
  line 
  passing 
  through 
  the 
  standard 
  compass. 
  

  

  The 
  coefficient 
  x> 
  or 
  heeling- 
  error, 
  which 
  in 
  these 
  ships 
  is 
  to 
  leeward, 
  

   and 
  practically 
  dependent 
  alone 
  upon 
  the 
  value 
  of 
  p 
  (X 
  being 
  so 
  near 
  

   unity 
  and 
  D 
  so 
  small), 
  of 
  course 
  becomes 
  greater 
  in 
  the 
  1 
  Undaunted 
  ' 
  

   than 
  in 
  the 
  two 
  other 
  ships. 
  

  

  So 
  far 
  all 
  the 
  coefficients 
  at 
  the 
  standard 
  compasses, 
  and 
  X, 
  /i, 
  and 
  \ 
  

   at 
  all 
  compasses, 
  have 
  been 
  examined 
  ; 
  there 
  remain 
  therefore 
  the 
  A, 
  B, 
  

  

  