﻿554 
  

  

  Mr. 
  E. 
  J. 
  Stone 
  on 
  Magnetical 
  [June 
  17, 
  

  

  any 
  kind 
  for 
  the 
  instruments 
  or 
  the 
  observer, 
  although 
  at 
  a 
  considerable 
  

   cost 
  in 
  time 
  and 
  in 
  the 
  comfort 
  of 
  those 
  engaged 
  upon 
  the 
  work. 
  The 
  

   greatest 
  trouble 
  arises 
  from 
  the 
  action 
  of 
  the 
  wind 
  upon 
  the 
  instruments, 
  

   more 
  particularly 
  upon 
  the 
  dip-instrument 
  ; 
  but 
  by 
  patiently 
  awaiting 
  

   opportunities 
  the 
  injurious 
  effects 
  arising 
  from 
  this 
  cause 
  can 
  be 
  very 
  

   nearly, 
  if 
  not 
  quite 
  eliminated. 
  I 
  decided 
  also, 
  after 
  some 
  hesitation, 
  

   to 
  take 
  no 
  assistant 
  with 
  me. 
  I 
  was 
  anxious 
  to 
  avoid 
  unnecessary 
  ex- 
  

   pense, 
  and 
  to 
  obtain 
  as 
  great 
  freedom 
  for 
  moving 
  about 
  the 
  country 
  as 
  

   possible. 
  I 
  only 
  absolutely 
  required 
  some 
  one 
  to 
  enter 
  the 
  times 
  from 
  a 
  

   chronometer 
  to 
  the 
  nearest 
  half-second; 
  and 
  I 
  found, 
  after 
  a 
  careful 
  

   series 
  of 
  experiments 
  upon 
  the 
  point, 
  that 
  my 
  wife 
  could 
  do 
  this 
  without 
  

   any 
  difficulty. 
  The 
  probable 
  error 
  of 
  these 
  time 
  determinations 
  does 
  not 
  

   appear 
  to 
  exceed 
  three 
  tenths 
  of 
  a 
  second 
  ; 
  and 
  it 
  would 
  be 
  very 
  difficult, 
  

   with 
  a 
  skilled 
  assistant, 
  to 
  obtain, 
  under 
  the 
  circumstances 
  of 
  these 
  

   observations, 
  a 
  much 
  greater 
  degree 
  of 
  accuracy. 
  The 
  instrumental 
  

   equipment 
  consisted 
  of 
  : 
  — 
  a 
  " 
  Dip," 
  by 
  Dover 
  ; 
  a 
  " 
  Unifilar," 
  variation, 
  and 
  

   intensity 
  instrument 
  combined, 
  by 
  Elliott 
  Brothers 
  ; 
  a 
  five-inch 
  Theodo- 
  

   lite, 
  for 
  the 
  determination 
  of 
  the 
  latitudes, 
  local 
  times, 
  and 
  absolute 
  

   azimuths 
  of 
  marks 
  ; 
  aneroid 
  barometer 
  ; 
  thermometer 
  ; 
  and 
  a 
  pocket 
  

   chronometer 
  beating 
  half-seconds. 
  With 
  only 
  two 
  persons 
  and 
  this 
  

   instrumental 
  equipment, 
  it 
  was 
  found 
  possible 
  to 
  move 
  freely 
  about 
  the 
  

   country 
  in 
  a 
  Cape 
  cart, 
  and 
  with 
  comparative 
  luxury 
  in 
  a 
  waggon. 
  

  

  I 
  knew 
  that 
  a 
  chronometer 
  could 
  not 
  be 
  trusted 
  to 
  carry 
  accurate 
  time 
  

   over 
  such 
  a 
  country 
  as 
  Namaqualand 
  without, 
  at 
  least, 
  special 
  appliances, 
  

   which 
  were 
  not 
  available 
  to 
  me 
  under 
  the 
  circumstances 
  of 
  the 
  case. 
  I 
  

   arranged 
  therefore 
  for 
  the 
  determination 
  of 
  local 
  time 
  with 
  the 
  theodolite, 
  

   and 
  for 
  the 
  fixing 
  of 
  the 
  absolute 
  azimuths 
  of 
  the 
  marks 
  with 
  the 
  same 
  

   theodolite 
  immediately 
  before 
  or 
  after 
  the 
  determinations 
  of 
  local 
  time. 
  

   The 
  ill 
  effects 
  of 
  a 
  trip 
  or 
  stoppage 
  of 
  the 
  chronometer 
  was 
  thus 
  elimi- 
  

   nated. 
  This 
  precaution 
  was 
  found 
  necessary. 
  The 
  chronometer 
  has 
  

   stopped 
  and 
  then 
  gone 
  on 
  again 
  on 
  several 
  occasions 
  from 
  the 
  dreadful 
  

   shaking 
  of 
  the 
  carts 
  or 
  waggons 
  over 
  the 
  rocky 
  roads, 
  and 
  has 
  on 
  some 
  

   occasions 
  tripped 
  some 
  seconds 
  from 
  merely 
  being 
  carried 
  about 
  in 
  the 
  

   pocket 
  or 
  hand. 
  The 
  chronometer 
  dead-beat 
  escapement 
  does 
  not 
  appear 
  

   at 
  all 
  well 
  fitted 
  for 
  rough 
  work 
  of 
  the 
  kind, 
  and 
  a 
  good 
  lever 
  escape- 
  

   ment 
  would 
  be 
  much 
  preferable. 
  The 
  chronometer 
  used 
  has 
  had 
  a 
  very 
  

   steady 
  rate 
  when 
  not 
  moved 
  about, 
  and 
  has 
  not 
  much 
  changed 
  that 
  rate, 
  

   when 
  at 
  rest, 
  from 
  the 
  effects 
  of 
  the 
  journey. 
  The 
  greatest 
  practical 
  

   inconvenience 
  experienced 
  in 
  the 
  use 
  of 
  the 
  instruments 
  was 
  the 
  occa- 
  

   sional 
  breakage 
  of 
  the 
  suspension-threads 
  and 
  the 
  loss 
  of 
  time 
  in 
  getting 
  

   the 
  new 
  threads 
  out 
  of 
  torsion. 
  After 
  several 
  accidents 
  of 
  the 
  kind, 
  1 
  

   used 
  three 
  instead 
  of 
  two 
  threads 
  of 
  suspension 
  ; 
  but 
  the 
  torsion 
  was 
  

   inconveniently 
  large, 
  and 
  the 
  loss 
  of 
  time 
  in 
  getting 
  the 
  threads 
  out 
  of 
  

   torsion 
  considerable. 
  These 
  three 
  threads 
  were 
  only 
  used 
  at 
  the 
  Orange- 
  

   River 
  station 
  and 
  on 
  the 
  return 
  to 
  Port 
  Nolloth. 
  The 
  time 
  of 
  vibration 
  

  

  