﻿OF 
  TERRESTRIAL 
  MAGNETISM 
  AT 
  SEVERAL 
  PLACES, 
  ETC. 
  443 
  

  

  The 
  progress 
  of 
  intensity 
  within 
  doors, 
  as 
  shown 
  by 
  observations 
  1 
  

   and 
  4, 
  is 
  contrary 
  to 
  that 
  of 
  the 
  ordinary 
  diurnal 
  variation. 
  This 
  was 
  

   correct, 
  however, 
  as 
  was 
  shown 
  by 
  six 
  sets 
  of 
  observations 
  between 
  3 
  h. 
  

   51' 
  and 
  5 
  h. 
  49', 
  at 
  temperatures 
  between 
  83.3 
  and 
  91.8°. 
  The 
  time 
  

   often 
  oscillations 
  diminished 
  from 
  32.115 
  to 
  32.035. 
  

  

  The 
  same 
  fact 
  recurs 
  in 
  the 
  observations 
  on 
  the 
  4th 
  of 
  February. 
  

   From 
  these, 
  numbered 
  5, 
  6 
  and 
  7, 
  allowing 
  for 
  the 
  diurnal 
  change 
  of 
  

   intensity 
  deduced 
  from 
  5 
  and 
  7, 
  the 
  value 
  of 
  m, 
  for 
  needle 
  B, 
  is, 
  

   m 
  = 
  .000,357. 
  

  

  This 
  supposes 
  7 
  to 
  be 
  reduced 
  to 
  the 
  temperature 
  of 
  5, 
  by 
  an 
  ap- 
  

   proximate 
  coefficient. 
  

  

  The 
  correction 
  obtained 
  in 
  1834 
  for 
  this 
  same 
  needle 
  was 
  

   m 
  = 
  .000,277. 
  

  

  It 
  would 
  seem 
  to 
  be 
  rather 
  more 
  susceptible 
  to 
  changes 
  of 
  tempera- 
  

   ture 
  now 
  than 
  at 
  the 
  former 
  time. 
  The 
  difference 
  however 
  is 
  small, 
  

   amounting 
  to 
  about 
  .04 
  of 
  a 
  second 
  in 
  ten 
  vibrations, 
  for 
  ten 
  degrees 
  

   of 
  the 
  thermometer. 
  

  

  The 
  coefficients 
  used 
  in 
  correcting 
  the 
  observations 
  which 
  follow, 
  

   are 
  brought 
  together 
  in 
  the 
  following 
  table. 
  

  

  TABLE 
  V. 
  

  

  Correction 
  for 
  Temperature 
  of 
  Needles 
  1, 
  2, 
  B, 
  A 
  and 
  C. 
  

  

  First 
  Series. 
  

  

  Value 
  of 
  m. 
  

  

  Second 
  Series. 
  

  

  Value 
  of 
  m. 
  

  

  Needle 
  No. 
  1 
  

  

  2 
  

  

  " 
  3 
  

  

  .000,436 
  

   .000,423 
  

   .000,277 
  

  

  Needle 
  A 
  

   " 
  C 
  

  

  3 
  (B) 
  

  

  .000,117 
  

   .000,052 
  

   .000,357 
  

  

  As 
  far 
  as 
  we 
  may 
  be 
  allowed 
  to 
  infer 
  from 
  these 
  observations, 
  the 
  

   correction 
  for 
  temperature 
  depends 
  for 
  its 
  amount 
  upon 
  the 
  degree 
  of 
  

   hardness, 
  or 
  temper, 
  of 
  the 
  material 
  of 
  the 
  needle 
  ; 
  in 
  other 
  words, 
  

   upon 
  the 
  same 
  property 
  which 
  causes 
  a 
  needle 
  to 
  retain 
  or 
  to 
  lose 
  a 
  

   charge 
  once 
  given 
  to 
  it. 
  

  

  Nos. 
  1 
  and 
  2, 
  of 
  different 
  dimensions, 
  but 
  of 
  the 
  same 
  material, 
  

  

  have 
  sensibly 
  the 
  same 
  correction. 
  C, 
  which 
  is 
  certainly 
  the 
  hardest 
  

  

  of 
  the 
  set, 
  has 
  a 
  very 
  small 
  correction. 
  The 
  prismatic 
  bar 
  A 
  has 
  a 
  

  

  correction 
  intermediate 
  between 
  the 
  two 
  cylinders 
  G 
  and 
  3 
  (B), 
  which 
  

  

  vol. 
  v. 
  — 
  5 
  o 
  

  

  