﻿TRANSACTIONS 
  

  

  OF 
  

  

  THE 
  AMERICAN 
  PHILOSOPHICAL 
  SOCIETY. 
  

  

  ARTICLE 
  I. 
  

  

  On 
  the 
  Diurnal 
  Variation 
  of 
  the 
  Horizontal 
  Needle. 
  By 
  Alexander 
  

   Dallas 
  Bache, 
  Professor 
  of 
  Natural 
  Philosophy 
  anil 
  Chemistry 
  in 
  

   the 
  University 
  of 
  Pennsylvania. 
  Read 
  November 
  16, 
  1832. 
  

  

  During 
  the 
  month 
  of 
  August, 
  and 
  part 
  of 
  September, 
  of 
  this 
  year, 
  

   the 
  usual 
  summer 
  vacation 
  of 
  the 
  University 
  permitted 
  my 
  absence 
  

   from 
  the 
  city, 
  and 
  finding 
  myself 
  favourably 
  situated 
  for 
  meteorologi- 
  

   cal 
  observations, 
  I 
  undertook 
  to 
  observe 
  the 
  diurnal 
  fluctuation 
  of 
  the 
  

   barometer 
  and 
  thermometer, 
  and, 
  ultimately, 
  the 
  hourly 
  variation 
  of 
  

   the 
  horizontal 
  needle. 
  It 
  was 
  a 
  source 
  of 
  great 
  regret 
  to 
  me, 
  that, 
  in 
  

   these 
  latter 
  observations, 
  I 
  was 
  not 
  also 
  furnished 
  with 
  a 
  dipping 
  

   needle, 
  or 
  with 
  the 
  means 
  of 
  directly 
  measuring 
  the 
  variation 
  of 
  mag- 
  

   netic 
  intensity: 
  the 
  observations 
  could 
  all 
  have 
  been 
  accomplished 
  

   with 
  little 
  more 
  inconvenience 
  than 
  the 
  hourly 
  observations 
  of 
  the 
  

   horizontal 
  needle 
  gave 
  ; 
  and 
  the 
  last 
  named 
  subject 
  is 
  more 
  interesting 
  

   than 
  the 
  point 
  which 
  I 
  was 
  enabled 
  to 
  observe. 
  This 
  being 
  the 
  case, 
  

   I 
  had 
  determined 
  not 
  to 
  make 
  public 
  these 
  observations, 
  but 
  to 
  use 
  

   vol. 
  v. 
  — 
  A 
  

  

  