﻿OF 
  TERRESTRIAL 
  MAGNETISM 
  AT 
  SEVERAL 
  PLACES, 
  ETC. 
  437 
  

  

  The 
  time 
  was 
  observed 
  by 
  a 
  good 
  pocket 
  chronometer, 
  making 
  one 
  

   hundred 
  and 
  fifty 
  beats 
  per 
  minute, 
  and 
  the 
  observed 
  times 
  of 
  beginning 
  

   and 
  end 
  are 
  given 
  to 
  four-tenths, 
  and 
  probably 
  with 
  accuracy 
  even 
  to 
  

   two-tenths 
  of 
  a 
  second. 
  

  

  The 
  irregularity 
  in 
  the 
  number 
  of 
  vibrations 
  between 
  two 
  given 
  

   arcs 
  was 
  observed 
  very 
  generally 
  in 
  the 
  first 
  series 
  of 
  experiments, 
  and 
  

   is 
  probably, 
  in 
  a 
  great 
  measure, 
  due 
  to 
  the 
  imperfect 
  mode 
  of 
  estimat- 
  

   ing 
  the 
  arcs. 
  It 
  has 
  little 
  or 
  no 
  effect 
  on 
  the 
  accuracy 
  of 
  the 
  results, 
  

   since 
  even 
  at 
  the 
  largest 
  arcs 
  many 
  successive 
  vibrations 
  will 
  be 
  per- 
  

   formed 
  in 
  times 
  not 
  differing 
  appreciably 
  from 
  each 
  other. 
  

  

  The 
  coefficient 
  for 
  the 
  correction 
  for 
  temperature 
  of 
  needle 
  No. 
  1, 
  

   as 
  deduced 
  from 
  the 
  experiments 
  just 
  given, 
  is, 
  

  

  From 
  experiments 
  1 
  and 
  3, 
  m 
  = 
  .000,455 
  

  

  1 
  " 
  4, 
  m 
  = 
  .000,427 
  

  

  2 
  « 
  3, 
  m 
  = 
  .000,446 
  

   2 
  " 
  4, 
  m 
  = 
  .000,417 
  

  

  Mean, 
  m 
  — 
  .000,436 
  

  

  Although 
  it 
  appears 
  rather 
  obvious 
  that 
  these 
  several 
  corrections 
  do 
  

   not 
  differ 
  essentially 
  from 
  the 
  mean, 
  it 
  may 
  not 
  be 
  amiss 
  to 
  show 
  that 
  

   the 
  difference 
  in 
  the 
  time 
  of 
  ten 
  vibrations 
  produced 
  by 
  using 
  either 
  

   of 
  them, 
  is 
  within 
  the 
  probable 
  limit 
  of 
  accuracy 
  of 
  the 
  separate 
  ob- 
  

   servations. 
  By 
  applying 
  the 
  first 
  coefficient, 
  which 
  differs 
  more 
  from 
  

   the 
  mean 
  than 
  either 
  the 
  second 
  or 
  third, 
  to 
  deduce 
  the 
  time 
  of 
  ten 
  

   vibrations 
  at 
  98° 
  Fah. 
  from 
  the 
  observed 
  time 
  at 
  33.6, 
  as 
  given 
  in 
  the 
  

   preceding 
  table, 
  we 
  have 
  46.58 
  seconds 
  : 
  while 
  the 
  mean 
  coefficient 
  

   similarly 
  applied, 
  gives 
  46.52 
  seconds, 
  differing 
  but 
  .06 
  of 
  a 
  second 
  in 
  

   the 
  time 
  of 
  ten 
  vibrations. 
  If 
  now 
  it 
  be 
  considered 
  that 
  these 
  ex- 
  

   tremes 
  of 
  temperature 
  are 
  much 
  further 
  apart 
  than 
  in 
  the 
  cases 
  oc- 
  

   curring 
  in 
  the 
  use 
  of 
  the 
  needles, 
  and 
  further 
  that 
  the 
  observations 
  are 
  

   to 
  be 
  reduced 
  to 
  a 
  selected 
  mean 
  temperature, 
  the 
  result 
  seems 
  entirely 
  

   satisfactory. 
  

  

  The 
  coefficient 
  for 
  the 
  reduction 
  for 
  temperature 
  of 
  needle 
  No. 
  

   2, 
  deduced 
  from 
  experiments 
  five 
  and 
  six 
  of 
  the 
  foregoing 
  tables, 
  is, 
  

   m 
  = 
  .000,423. 
  That 
  for 
  No. 
  3, 
  is 
  m" 
  = 
  000,277. 
  

  

  