﻿OF 
  TERRESTRIAL 
  MAGNETISM 
  AT 
  SEVERAL 
  PLACES, 
  ETC. 
  

  

  457 
  

  

  From 
  these 
  are 
  deduced 
  the 
  horizontal 
  intensities 
  given 
  below 
  : 
  the 
  

   relative 
  weights 
  of 
  the 
  observations, 
  considering 
  them 
  to 
  be 
  liable 
  to 
  

   the 
  same 
  mean 
  error, 
  and 
  the 
  mean 
  horizontal 
  intensities 
  deduced 
  from 
  

   a 
  comparison 
  of 
  the 
  different 
  results 
  according 
  to 
  their 
  weights, 
  are 
  as 
  

   follows. 
  

  

  Places. 
  

  

  Relative 
  Horizontal 
  

   Intensities 
  by 
  Needle. 
  

  

  Weights 
  of 
  Observa- 
  

   tion 
  by 
  Needle. 
  

  

  Mean 
  Horizontal 
  

   Intensities. 
  

  

  A 
  

  

  C 
  

  

  No. 
  3 
  

  

  A 
  

  

  C 
  

  

  No. 
  3 
  

  

  Providence, 
  R. 
  I. 
  

  

  Springfield, 
  Mass. 
  

   Albany, 
  N. 
  Y. 
  

  

  .89637 
  

   .88703 
  

   .85226 
  

  

  .89773 
  

   .88673 
  

   .85394 
  

  

  .90492 
  

  

  .88794 
  

  

  508 
  

   678 
  

   682 
  

  

  428 
  

   424 
  

   424 
  

  

  254 
  

   255 
  

  

  .89869 
  

   .88711 
  

   .85290 
  

  

  ON 
  THE 
  TOTAL 
  MAGNETIC 
  INTENSITY. 
  

  

  We 
  have 
  already 
  remarked, 
  that 
  we 
  do 
  not 
  consider 
  the 
  dip 
  to 
  be 
  

   sufficiently 
  well 
  known 
  at 
  any 
  of 
  the 
  places 
  at 
  which 
  we 
  have 
  de- 
  

   duced 
  the 
  horizontal 
  intensities, 
  to 
  admit 
  of 
  combining 
  the 
  results 
  for 
  

   the 
  total 
  intensity. 
  For 
  example, 
  at 
  Albany 
  the 
  difference 
  of 
  eleven 
  

   minutes 
  between 
  our 
  observations 
  and 
  those 
  of 
  professor 
  Henry, 
  cor- 
  

   responds 
  to 
  a 
  difference 
  in 
  intensity 
  of 
  0.01177. 
  The 
  places 
  at 
  which 
  

   the 
  observations 
  were 
  made 
  lie 
  so 
  nearly 
  upon 
  the 
  line 
  of 
  equal 
  inten- 
  

   sity 
  as 
  to 
  render 
  so 
  rude 
  an 
  approximation 
  entirely 
  inadmissible. 
  The 
  

   general 
  direction 
  thus 
  pointed 
  out 
  for 
  this 
  line, 
  accords 
  with 
  the 
  gene- 
  

   ral 
  direction 
  formerly 
  assigned 
  by 
  captain 
  Sabine.* 
  

  

  * 
  American 
  Jour. 
  Science, 
  Vol. 
  XXII. 
  Letter 
  to 
  Professor 
  Renwick. 
  

  

  