﻿1875.] 
  

  

  Effects 
  of 
  Iron 
  Masts 
  on 
  Compasses. 
  

  

  583 
  

  

  tects. 
  In 
  these 
  papers 
  may 
  be 
  traced 
  in 
  turn 
  the 
  effects 
  of 
  adding 
  steam- 
  

   engines 
  and 
  boilers, 
  iron 
  beams, 
  and 
  armour 
  plating 
  ; 
  but 
  until 
  lately 
  no 
  

   good 
  opportunity 
  has 
  occurred 
  for 
  accurately 
  denning 
  the 
  action 
  of 
  iron 
  

   masts 
  in 
  producing 
  compass 
  disturbance 
  from 
  observation. 
  The 
  case 
  

   referred 
  to 
  is 
  that 
  of 
  H.M.S. 
  ' 
  Undaunted 
  and 
  when 
  about 
  to 
  visit 
  that 
  

   ship 
  in 
  the 
  ordinary 
  course 
  of 
  my 
  duties 
  in 
  the 
  Compass 
  Department, 
  I 
  

   was 
  directed 
  by 
  the 
  Hydrographer 
  to 
  make 
  a 
  special 
  series 
  of 
  observa- 
  

   tions 
  of 
  the 
  horizontal 
  and 
  vertical 
  forces 
  at 
  all 
  three 
  compasses, 
  as 
  the 
  

   lower 
  masts 
  and 
  bowsprit 
  were 
  of 
  iron. 
  

  

  To 
  prepare 
  the 
  way 
  for 
  a 
  discussion 
  of 
  the 
  results 
  of 
  these 
  observa- 
  

   tions, 
  it 
  appears 
  necessary 
  to 
  give 
  a 
  short 
  history 
  of 
  the 
  two 
  principal 
  

   vessels 
  mentioned 
  in 
  this 
  paper, 
  and 
  also 
  to 
  go 
  over 
  some 
  already 
  well- 
  

   trodden 
  ground, 
  whilst 
  taking 
  account 
  of 
  all 
  the 
  iron 
  and 
  the 
  effects 
  on 
  

   their 
  compasses, 
  until 
  the 
  question 
  of 
  the 
  iron 
  masts 
  alone 
  remains 
  to 
  be 
  

   settled. 
  

  

  Eor 
  some 
  years 
  past 
  there 
  have 
  been 
  lying 
  in 
  Sheerness 
  harbour 
  two 
  

   wooden 
  frigates 
  of 
  exactly 
  the 
  same 
  build, 
  tonnage, 
  and 
  horse-power, 
  

   namely, 
  the 
  ' 
  Undaunted' 
  and 
  'Newcastle' 
  — 
  the 
  only 
  important 
  difference 
  

   between 
  them 
  being 
  that 
  the 
  'Undaunted' 
  has 
  iron 
  masts, 
  the 
  'New- 
  

   castle' 
  wooden. 
  The 
  diagonal 
  irou 
  riders 
  which 
  form 
  the 
  principal 
  por- 
  

   tion 
  of 
  the 
  iron 
  used 
  in 
  construction 
  of 
  their 
  hulls 
  are 
  about 
  6 
  inches 
  in 
  

   breadth, 
  J 
  of 
  an 
  inch 
  thick, 
  and 
  placed 
  5 
  feet 
  apart, 
  at 
  an 
  angle 
  of 
  45° 
  

   with 
  the 
  decks. 
  They 
  extend 
  from 
  about 
  5 
  feet 
  from 
  the 
  keelson 
  on 
  

   both 
  sides 
  of 
  the 
  ship 
  up 
  to 
  the 
  top 
  sides 
  — 
  the 
  after 
  riders 
  inclined 
  

   towards 
  the 
  bow, 
  the 
  foremost 
  towards 
  the 
  stern, 
  the 
  two 
  sets 
  meeting 
  

   and 
  overlapping 
  amidships. 
  These 
  riders, 
  therefore, 
  being 
  separated 
  are 
  

   independent 
  magnets, 
  except 
  at 
  the 
  point 
  of 
  meeting 
  just 
  mentioned. 
  

  

  The 
  'Newcastle' 
  was 
  built 
  at 
  Deptford, 
  head 
  S. 
  73° 
  W. 
  (magnetic), 
  

   and 
  is 
  a 
  vessel 
  of 
  3035 
  tons 
  and 
  600 
  horse-power. 
  The 
  ' 
  Undaunted 
  ' 
  

   was 
  built 
  at 
  Chatham, 
  head 
  S. 
  43° 
  E. 
  (magnetic), 
  and 
  is 
  a 
  vessel 
  of 
  

   3039 
  tons 
  and 
  600 
  horse-power. 
  Assuming 
  the 
  dip 
  at 
  the 
  time 
  of 
  

   building 
  to 
  be 
  68°, 
  the 
  after 
  riders 
  of 
  both 
  ships 
  (near 
  which 
  the 
  com- 
  

   passes 
  are 
  placed) 
  were 
  not 
  far 
  removed 
  from 
  the 
  direction 
  of 
  the 
  Earth's 
  

   Total 
  Eorce, 
  and 
  would 
  therefore 
  become 
  strongly 
  magnetized, 
  especially 
  

   those 
  in 
  the 
  ' 
  Undaunted.' 
  

  

  A 
  glance 
  at 
  the 
  coefficient 
  C 
  of 
  the 
  standard 
  compasses 
  given 
  in 
  the 
  

   Table 
  shows 
  at 
  once 
  which 
  ship 
  was 
  built 
  in 
  the 
  easterly 
  and 
  which 
  in 
  

   the 
  westerly 
  direction; 
  and, 
  further, 
  it 
  is 
  highly 
  probable 
  that 
  in 
  the 
  

   ' 
  Newcastle' 
  the 
  coefficient 
  B 
  would 
  have 
  been 
  more 
  nearly 
  in 
  accordance 
  

   with 
  the 
  results 
  of 
  direction 
  of 
  the 
  ship 
  in 
  building, 
  but 
  for 
  the 
  masses 
  

   of 
  iron 
  introduced 
  in 
  equipment, 
  such 
  as 
  engines 
  and 
  boilers, 
  armament, 
  

   great 
  funnel, 
  &c. 
  In 
  fact, 
  as 
  the 
  compass 
  is 
  only 
  62 
  feet 
  from 
  the 
  stern, 
  

   there 
  is 
  a 
  large 
  excess 
  of 
  iron 
  before 
  that 
  position 
  compared 
  with 
  that 
  abaft. 
  

   "We 
  may 
  reasonably 
  assume 
  the 
  same 
  of 
  the 
  B 
  in 
  the 
  ' 
  Undaunted' 
  before 
  

   her 
  iron 
  masts 
  were 
  stepped. 
  

  

  