﻿ARTICLE 
  XXVIII. 
  

  

  On 
  the 
  Relative 
  Horizontal 
  Intensities 
  of 
  Terrestrial 
  Magnetism 
  at 
  

   several 
  F 
  laces 
  in 
  the 
  United 
  States, 
  with 
  the 
  Investigation 
  of 
  Correc- 
  

   tions 
  for 
  Temperature, 
  and 
  Comparisons 
  of 
  the 
  Methods 
  of 
  Oscillation 
  

   in 
  Full 
  and 
  in 
  Marefied 
  Air. 
  By 
  A. 
  D. 
  Bache, 
  Professor 
  of 
  Natural 
  

   Philosophy 
  and 
  Chemistry, 
  and 
  Edward 
  H. 
  Courtenay, 
  Professor 
  of 
  

   Mathematics, 
  in 
  the 
  University 
  of 
  Pennsylvania. 
  Mead 
  May 
  6th, 
  1836. 
  

  

  The 
  observations 
  for 
  horizontal 
  intensity 
  which 
  we 
  are 
  about 
  to 
  

   present 
  to 
  the 
  Society 
  were 
  commenced 
  in 
  the 
  spring 
  of 
  1834, 
  and 
  

   have 
  been 
  continued 
  at 
  intervals 
  since 
  that 
  time. 
  The 
  first 
  series 
  

   was 
  made 
  w 
  r 
  ith 
  the 
  usual 
  apparatus, 
  namely, 
  a 
  needle, 
  suspended 
  by 
  a 
  

   fibre 
  without 
  torsion, 
  and 
  made 
  to 
  vibrate 
  in 
  a 
  closed 
  box. 
  The 
  

   second 
  series 
  was 
  obtained 
  by 
  oscillating 
  the 
  needles 
  in 
  rarefied 
  air. 
  

   These 
  latter 
  observations 
  having 
  proved 
  satisfactory, 
  we 
  should 
  be 
  able 
  

   to 
  determine 
  the 
  total 
  intensities 
  at 
  the 
  several 
  places 
  of 
  observation, 
  

   were 
  the 
  dip 
  determined 
  with 
  a 
  sufficient 
  degree 
  of 
  minuteness. 
  

   While 
  our 
  observations 
  with 
  the 
  ordinary 
  dipping-needle 
  already 
  pub- 
  

   lished 
  by 
  the 
  Society,* 
  show 
  approximately 
  the 
  variations 
  of 
  that 
  ele- 
  

   ment, 
  a 
  minute 
  variation 
  in 
  the 
  angle 
  affects, 
  when 
  the 
  dip 
  is 
  so 
  large, 
  

   so 
  considerably 
  the 
  total 
  intensity, 
  that 
  we 
  do 
  not 
  feel 
  warranted 
  at 
  

   present 
  in 
  combining 
  those 
  results 
  with 
  the 
  horizontal 
  forces. 
  

  

  * 
  American 
  Philosophical 
  Society's 
  Transactions, 
  Vol. 
  V., 
  (Part 
  II.) 
  page 
  309. 
  

   VOL. 
  V. 
  5 
  K 
  

  

  