﻿438 
  ON 
  THE 
  RELATIVE 
  HORIZONTAL 
  INTENSITIES 
  

  

  No 
  permanent 
  change 
  in 
  the 
  magnetic 
  state 
  of 
  either 
  of 
  the 
  needles 
  

   was 
  produced 
  by 
  the 
  elevation 
  of 
  temperature 
  to 
  which 
  they 
  were 
  

   subjected 
  in 
  these 
  experiments. 
  

  

  In 
  the 
  Second 
  Series 
  of 
  observations, 
  the 
  correction 
  for 
  temperature 
  

   of 
  Needle 
  A, 
  was 
  obtained 
  immediately 
  after 
  the 
  observations 
  at 
  the 
  

   different 
  stations 
  had 
  been 
  completed. 
  As 
  in 
  the 
  experiments 
  already 
  

   given, 
  the 
  temperature 
  of 
  the 
  needle 
  was 
  lowered 
  by 
  ice, 
  and 
  raised 
  by 
  

   the 
  heat 
  from 
  spirit 
  lamps, 
  placed 
  in 
  the 
  same 
  inclosure 
  with 
  the 
  jar. 
  

  

  It 
  was 
  not 
  convenient 
  to 
  observe 
  the 
  other 
  needles 
  at 
  the 
  same 
  time, 
  

   and 
  the 
  corrections 
  applied 
  to 
  them 
  were 
  obtained 
  in 
  February, 
  and 
  

   within 
  doors. 
  Two 
  questions 
  were 
  thus 
  suggested 
  : 
  first, 
  whether 
  the 
  

   correction 
  for 
  temperature 
  is 
  sensibly 
  the 
  same 
  at 
  different 
  seasons, 
  or 
  

   whether 
  a 
  variation 
  in 
  the 
  earth's 
  magnetic 
  intensity 
  may 
  produce 
  a 
  

   change 
  in 
  the 
  distribution 
  of 
  the 
  magnetism 
  of 
  a 
  needle, 
  so 
  as 
  to 
  ren- 
  

   der 
  it 
  more 
  or 
  less 
  liable 
  to 
  have 
  its 
  state 
  changed 
  by 
  heat. 
  Second, 
  

   whether 
  the 
  local 
  magnetism 
  proportionably 
  affects 
  the 
  magnetic 
  state 
  

   of 
  a 
  needle 
  at 
  different 
  temperatures. 
  As 
  far 
  as 
  the 
  practical 
  use 
  of 
  

   the 
  correction 
  for 
  our 
  observations 
  is 
  concerned, 
  both 
  these 
  questions 
  

   were 
  resolved. 
  And 
  from 
  the 
  answer, 
  we 
  felt 
  warranted 
  in 
  deducing 
  

   the 
  corrections 
  for 
  the 
  needles 
  B 
  and 
  C, 
  as 
  above 
  stated. 
  

  

  All 
  the 
  observations 
  were 
  made 
  with 
  the 
  same 
  thermometer 
  which 
  

   was 
  used 
  to 
  give 
  the 
  temperature 
  of 
  experiment 
  of 
  the 
  different 
  stations. 
  

   The 
  observations 
  for 
  the 
  correction 
  for 
  needle 
  A, 
  are 
  contained 
  in 
  

   the 
  following 
  table, 
  of 
  which 
  the 
  form 
  is 
  similar 
  to 
  that 
  before 
  given. 
  

   A 
  column 
  is 
  introduced 
  for 
  the 
  height 
  of 
  the 
  gauge, 
  and 
  two 
  others 
  to 
  

   contain 
  the 
  mean 
  of 
  the 
  separate 
  determinations 
  at 
  each 
  temperature. 
  

  

  