﻿ARTICLE 
  V11I. 
  

  

  Observations 
  to 
  determine 
  the 
  Magnetic 
  Dip 
  at 
  Baltimore, 
  Philadel- 
  

   phia, 
  New 
  York, 
  West 
  Point, 
  Providence, 
  Springfield 
  and 
  Mbany. 
  

   By 
  A. 
  D. 
  Bache, 
  Professor 
  of 
  Natural 
  Philosophy 
  and 
  Chemistry, 
  

   and 
  Edward 
  H. 
  Courtenay,* 
  Professor 
  of 
  Mathematics, 
  in 
  the 
  Univer- 
  

   sity 
  of 
  Pennsylvania. 
  Bead 
  November 
  7th, 
  1834. 
  

  

  The 
  following 
  observations 
  of 
  the 
  magnetic 
  dip 
  were 
  made 
  at 
  

   places 
  betw 
  T 
  een 
  the 
  latitudes 
  of 
  39° 
  17' 
  and 
  42° 
  39' 
  N. 
  and 
  longitudes 
  

   of 
  71° 
  25' 
  and 
  76° 
  28' 
  W. 
  In 
  all 
  of 
  them 
  a 
  dipping 
  needle 
  made 
  by 
  

   Gambey 
  for 
  the 
  apparatus 
  of 
  the 
  Military 
  Academy 
  at 
  West 
  Point 
  

   was 
  used. 
  This 
  needle 
  is 
  provided 
  with 
  all 
  the 
  adjustments 
  necessary 
  

   to 
  render 
  its 
  use 
  accurate, 
  and 
  its 
  performance 
  is 
  highly 
  satisfactory. 
  

   The 
  vertical 
  circle 
  upon 
  which 
  the 
  dip 
  is 
  read, 
  is 
  graduated 
  to 
  fifteen 
  

   minutes, 
  and 
  can 
  be 
  read 
  with 
  ease 
  to 
  five 
  minutes 
  by 
  the 
  aid 
  of 
  two 
  

   microscopes 
  attached 
  to 
  the 
  glass 
  case 
  which 
  covers 
  the 
  instrument. 
  

   The 
  horizontal 
  circle, 
  which 
  serves 
  to 
  mark 
  the 
  position 
  of 
  the 
  plane 
  

   perpendicular 
  to 
  the 
  magnetic 
  meridian, 
  and 
  hence 
  to 
  place 
  the 
  nee- 
  

   dle 
  in 
  the 
  meridian, 
  is 
  graduated 
  to 
  half 
  degrees, 
  and 
  reads 
  by 
  a 
  ver- 
  

   nier 
  to 
  two 
  minutes. 
  The 
  axis 
  of 
  the 
  needle 
  rests 
  upon 
  two 
  small 
  

   agate 
  supports, 
  and 
  its 
  uniform 
  position 
  upon 
  them 
  is 
  insured 
  by 
  two 
  

  

  * 
  Late 
  Professor 
  of 
  Natural 
  and 
  Experimental 
  Philosophy 
  at 
  the 
  United 
  States 
  Military- 
  

   Academy. 
  

  

  VOL. 
  V. 
  — 
  3 
  c 
  

  

  