﻿582 
  

  

  Staff- 
  Commander 
  E. 
  W. 
  Creak 
  on 
  the 
  

  

  [June 
  17, 
  

  

  It 
  would 
  thus 
  appear 
  that, 
  as 
  far 
  as 
  we 
  can 
  judge 
  from 
  these 
  obser- 
  

   vations, 
  there 
  is 
  more 
  solar 
  heat 
  at 
  London 
  in 
  years 
  of 
  maximum 
  than 
  in 
  

   years 
  of 
  minimum 
  disturbance. 
  

  

  This 
  agrees 
  very 
  well 
  with 
  a 
  remark 
  made 
  by 
  Messrs. 
  De 
  la 
  Eue, 
  

   Stewart, 
  and 
  Lowey, 
  the 
  Kew 
  Observers, 
  to 
  the 
  effect 
  that 
  the 
  number 
  

   of 
  fine 
  days 
  in 
  the 
  year 
  on 
  which 
  solar 
  pictures 
  might 
  be 
  taken 
  ap- 
  

   peared 
  to 
  be 
  greater 
  in 
  years 
  of 
  maximum 
  than 
  in 
  years 
  of 
  minimum 
  

   sun-spot 
  frequency. 
  

  

  XX. 
  " 
  On 
  the 
  Effects 
  of 
  Iron 
  Masts 
  on 
  Compasses 
  placed 
  near 
  

   them/' 
  By 
  Staff-Commander 
  E. 
  W. 
  Creak, 
  R,.N. 
  Com- 
  

   municated 
  by 
  Captain 
  Evans, 
  R.N., 
  F.R.S., 
  by 
  permission 
  of 
  

   the 
  Lords 
  Commissioners 
  of 
  the 
  Admiralty. 
  Received 
  June 
  

   17, 
  1875. 
  

  

  The 
  question 
  of 
  the 
  position 
  of 
  the 
  standard 
  compass 
  on 
  board 
  ship, 
  

   whether 
  of 
  wood 
  or 
  iron, 
  is 
  one 
  of 
  the 
  greatest 
  importance 
  with 
  respect 
  

   to 
  safe 
  navigation. 
  In 
  H.M. 
  ships 
  it 
  is 
  one 
  of 
  the 
  principal 
  duties 
  of 
  

   the 
  Superintendent 
  of 
  Compasses 
  to 
  secure 
  the 
  best 
  possible 
  position 
  for 
  

   this 
  compass, 
  and 
  when 
  that 
  position 
  has 
  been 
  determined, 
  to 
  ascertain 
  

   the 
  horizontal 
  and 
  vertical 
  components 
  of 
  the 
  total 
  magnetic 
  force 
  re- 
  

   sulting 
  from 
  the 
  iron 
  used 
  in 
  the 
  construction 
  and 
  equipment 
  of 
  every 
  

   class 
  of 
  vessel, 
  in 
  order 
  that 
  the 
  correctness 
  of 
  this 
  choice 
  of 
  position 
  

   may 
  be 
  insured 
  and 
  the 
  facts 
  recorded. 
  

  

  "With 
  proper 
  instruments 
  in 
  experienced 
  hands 
  these 
  observations 
  can 
  

   be 
  readily 
  made 
  ; 
  but 
  in 
  iron 
  ships 
  it 
  is 
  a 
  somewhat 
  intricate 
  matter 
  to 
  

   eliminate 
  the 
  part 
  which 
  the 
  hull 
  plays 
  in 
  producing 
  these 
  forces, 
  from 
  

   those 
  caused 
  by 
  iron 
  used 
  in 
  equipment, 
  unless 
  observations 
  are 
  made 
  on 
  

   completion 
  of 
  the 
  hull 
  and 
  afterwards 
  as 
  the 
  equipment 
  progresses. 
  In 
  

   wooden 
  ships, 
  however, 
  the 
  case 
  is 
  different 
  ; 
  for 
  the 
  great 
  mass 
  of 
  the 
  

   ship 
  being 
  of 
  wood 
  and 
  the 
  iron 
  in 
  detached 
  masses, 
  the 
  latter 
  can 
  be 
  

   attacked 
  in 
  detail, 
  and 
  the 
  disturbance 
  they 
  cause 
  to 
  the 
  several 
  com- 
  

   passes 
  nearly 
  observed. 
  

  

  Carefully 
  conducted 
  investigations 
  made 
  in 
  different 
  ships 
  on 
  the 
  

   effects 
  of 
  similar 
  bodies 
  of 
  iron 
  are 
  very 
  valuable 
  to 
  those 
  directing 
  com- 
  

   pass 
  arrangements, 
  as 
  they 
  give 
  the 
  necessary 
  information 
  as 
  to 
  how 
  

   near 
  those 
  bodies 
  may 
  be 
  approached 
  or 
  of 
  necessity 
  avoided. 
  

  

  The 
  effects 
  of 
  introducing 
  iron 
  riders 
  for 
  strengthening 
  wooden 
  ships 
  

   were 
  in 
  a 
  measure 
  discussed 
  by 
  the 
  late 
  Captain 
  E. 
  J. 
  Johnson 
  in 
  his 
  

   work 
  ' 
  On 
  the 
  Necessity 
  of 
  ascertaining 
  the 
  Deviation 
  of 
  the 
  Compass/ 
  

   where 
  he 
  treats 
  of 
  the 
  diagonal 
  iron 
  riders 
  of 
  the 
  ' 
  Encounter 
  ' 
  and 
  

   1 
  Conflict/ 
  but 
  afterwards 
  more 
  fully 
  in 
  the 
  papers 
  which 
  the 
  present 
  

   Hydrographer, 
  Captain 
  Evans, 
  E.E.S., 
  has 
  written 
  and 
  published 
  in 
  the 
  

   Philosophical 
  Transactions 
  of 
  the 
  Eoyal 
  Society, 
  Journal 
  of 
  the 
  United 
  

   Service 
  Institution, 
  and 
  Transactions 
  of 
  the 
  Institute 
  of 
  Naval 
  Archi- 
  

  

  