﻿1875.] 
  

  

  Effects 
  of 
  Iron 
  Masts 
  on 
  Compasses. 
  

  

  587 
  

  

  C, 
  D, 
  E 
  of 
  the 
  steering-compasses 
  to 
  be 
  considered. 
  Eor 
  this 
  purpose 
  

   there 
  is 
  sufficient 
  evidence 
  in 
  the 
  two 
  sister 
  ships, 
  which 
  are 
  strictly 
  

   comparable. 
  

  

  The 
  compasses 
  are 
  necessarily 
  placed 
  out 
  of 
  the 
  central 
  line 
  of 
  the 
  

   ships, 
  and 
  diagonally 
  to 
  the 
  mast 
  under 
  discussion 
  ; 
  therefore, 
  as 
  shown 
  

   by 
  the 
  figures 
  in 
  the 
  Table, 
  a 
  transverse 
  component 
  is 
  introduced. 
  In 
  

   effect 
  the 
  iron 
  mast 
  has 
  increased 
  the 
  B 
  of 
  the 
  ' 
  Undaunted's 
  ' 
  steering- 
  

   compasses 
  by 
  about 
  16°. 
  To 
  the 
  +C 
  of 
  her 
  starboard 
  steering-compass 
  

   about 
  11° 
  have 
  been 
  added, 
  and 
  at 
  the 
  port 
  steering 
  a 
  large 
  — 
  C 
  of 
  13 
  J° 
  

   shows 
  the 
  transverse 
  component 
  of 
  the 
  mast's 
  force 
  more 
  strongly 
  than 
  

   at 
  the 
  starboard 
  ; 
  but 
  the 
  2|° 
  in 
  excess 
  are 
  probably 
  due 
  to 
  some 
  other 
  

   cause 
  not 
  accounted 
  for 
  by 
  the 
  observations 
  made. 
  

  

  The 
  A 
  for 
  these 
  compasses 
  is 
  large 
  in 
  both 
  ships 
  ; 
  this 
  does 
  not, 
  how- 
  

   ever, 
  appear 
  to 
  proceed 
  from 
  magnetic 
  causes, 
  but 
  rather 
  from 
  mechanical 
  

   error 
  in 
  placing 
  the 
  binacles. 
  D 
  and 
  E 
  show 
  the 
  results 
  usual 
  in 
  

   wooden 
  ships, 
  except 
  the 
  D 
  in 
  the 
  * 
  Undaunted,' 
  which 
  is 
  slightly 
  

   increased. 
  

  

  Having 
  thus, 
  I 
  think, 
  defined 
  the 
  effects 
  of 
  the 
  iron 
  mizzenmast 
  of 
  the 
  

   'Undaunted' 
  on 
  her 
  compasses, 
  it 
  remains 
  now 
  to 
  show 
  what 
  was 
  the 
  

   most 
  desirable 
  way 
  of 
  meeting 
  them, 
  and 
  what 
  was 
  actually 
  done 
  in 
  that 
  

   direction. 
  

  

  The 
  most 
  certain 
  cure 
  of 
  the 
  evil 
  would 
  have 
  been 
  to 
  remove 
  all 
  the 
  

   compasses 
  further 
  away 
  from 
  the 
  mast, 
  as 
  far 
  as 
  magnetic 
  reasons 
  are 
  

   concerned 
  ; 
  but 
  this 
  would 
  have 
  entailed 
  serious 
  alterations 
  in 
  the 
  arrange- 
  

   ments 
  of 
  the 
  ship 
  which 
  the 
  occasion 
  by 
  no 
  means 
  warranted. 
  

  

  The 
  standard 
  compass 
  might 
  have 
  been 
  raised 
  to 
  a 
  level 
  with 
  the 
  

   neutral 
  zone 
  of 
  the 
  mast, 
  but 
  this 
  at 
  the 
  expense 
  of 
  increasing 
  vibration 
  

   in 
  the 
  card 
  from 
  greater 
  length 
  of 
  pedestal. 
  

  

  The 
  steering-compasses 
  being 
  in 
  the 
  most 
  suitable 
  position 
  for 
  the 
  use 
  

   of 
  the 
  helmsman, 
  and 
  there 
  being 
  the 
  standard 
  compass 
  as 
  a 
  means 
  of 
  

   comparison 
  and 
  obtaining 
  the 
  correct 
  course, 
  no 
  change 
  of 
  position 
  was 
  

   necessary. 
  The 
  three 
  compasses 
  were 
  therefore 
  corrected 
  by 
  magnets, 
  

   the 
  semicircular 
  deviation 
  being 
  reduced 
  to 
  the 
  same 
  amount 
  as 
  in 
  the 
  

   ' 
  Newcastle.' 
  It 
  was 
  not 
  thought 
  desirable 
  to 
  correct 
  the 
  whole 
  of 
  the 
  

   semicircular 
  deviation, 
  as 
  the 
  mast, 
  when 
  the 
  ship 
  should 
  make 
  large 
  

   changes 
  of 
  latitude, 
  would 
  probably 
  add 
  to 
  the 
  changing 
  part 
  of 
  that 
  

   deviation 
  observed 
  in 
  this 
  class 
  of 
  ships. 
  

  

  Conclusions. 
  

   The 
  effects 
  of 
  iron 
  masts 
  are 
  these 
  : 
  — 
  

  

  1. 
  They 
  produce 
  semicircular 
  deviation, 
  and 
  the 
  objectionable 
  addition 
  

   to 
  that 
  deviation 
  known 
  as 
  heeling-error. 
  

  

  2. 
  That 
  these 
  effects 
  need 
  not 
  always 
  be 
  avoided, 
  as 
  in 
  certain 
  cases 
  

   they 
  may 
  be 
  made 
  useful 
  in 
  experienced 
  hands 
  ; 
  for 
  example, 
  the 
  prin- 
  

   cipal 
  mast 
  in 
  this 
  discussion 
  (as 
  shown 
  in 
  the 
  accompanving 
  sketch, 
  p. 
  58S) 
  

   might, 
  in 
  an 
  iron 
  ship 
  built 
  head 
  north, 
  be 
  used 
  to 
  correct 
  the 
  — 
  B 
  of 
  

  

  