﻿254 
  Notices 
  respecting 
  New 
  Boohs. 
  

  

  given 
  to 
  recording 
  exact 
  times 
  on 
  the 
  magnetic 
  carves. 
  In 
  the 
  

   case 
  of 
  the 
  declination, 
  44 
  small 
  perturbations 
  were 
  identified 
  in 
  

   the 
  Haldde 
  and 
  Potsdam 
  curves. 
  In 
  no 
  case 
  did 
  the 
  apparent 
  

   difference 
  in 
  time 
  exceed 
  18 
  seconds, 
  and 
  in 
  38 
  of 
  the 
  44 
  cases 
  

   the 
  difference 
  did 
  not 
  exceed 
  10 
  seconds. 
  The 
  mean 
  apparent 
  

   difference 
  was 
  1 
  second. 
  As 
  Prof. 
  Birkeland 
  does 
  not 
  guarantee 
  

   accuracy 
  to 
  nearer 
  than 
  10 
  seconds, 
  practical 
  coincidence 
  in 
  

   time 
  seems 
  well 
  established. 
  The 
  importance 
  of 
  this 
  result 
  is 
  

   increased 
  by 
  the 
  very 
  considerable 
  distance 
  — 
  about 
  2000 
  kilo- 
  

   metres 
  — 
  between 
  the 
  two 
  stations. 
  Another 
  interesting 
  feature 
  

   was 
  the 
  occurrence 
  of 
  well-marked 
  magnetic 
  waves, 
  similar 
  to 
  

   those 
  to 
  whose 
  elucidation 
  so 
  much 
  has 
  been 
  done 
  by 
  Prof. 
  

   Eschenhagen, 
  whose 
  recent 
  death 
  is 
  a 
  serious 
  loss 
  to 
  Terrestrial 
  

   Magnetism. 
  

  

  At 
  first, 
  it 
  may 
  be 
  remembered, 
  Prof. 
  Eschenhagen's 
  observations 
  

   pointed 
  to 
  the 
  conclusion 
  that 
  these 
  waves 
  were 
  limited 
  to 
  one 
  or 
  

   two 
  approximately 
  constant 
  periods, 
  one 
  notably 
  of 
  30 
  seconds. 
  

   Prof. 
  Birkeland, 
  however, 
  gives, 
  pp. 
  8 
  & 
  9, 
  a 
  complete 
  list 
  of 
  all 
  

   the 
  : 
  ' 
  waves 
  " 
  recorded 
  by 
  the 
  quick-moving 
  apparatus 
  at 
  Potsdam 
  

   from 
  May 
  1898 
  to 
  May 
  1900, 
  and 
  this 
  shows 
  periods 
  of 
  all 
  lengths 
  

   from 
  7*8 
  to 
  125*0 
  seconds. 
  At 
  Haldde 
  the 
  average 
  periodic 
  time 
  

   would 
  seem 
  to 
  be 
  longer, 
  for 
  in 
  the 
  wave 
  series 
  observed 
  there 
  

   in 
  March 
  1900 
  the 
  periods 
  varied 
  from 
  62 
  to 
  130 
  seconds. 
  

   Waves 
  with 
  such 
  periods 
  have 
  been 
  of 
  course 
  copiously 
  recorded 
  

   by 
  Kew 
  pattern 
  magnetographs 
  during 
  the 
  last 
  40 
  years 
  ; 
  but 
  

   with 
  drums 
  run 
  at 
  the 
  usual 
  rate, 
  only 
  the 
  general 
  features 
  can 
  

   be 
  traced. 
  

  

  Whilst 
  arriving, 
  as 
  we 
  have 
  seen, 
  at 
  the 
  conclusion 
  that 
  dis- 
  

   tinctive 
  small 
  magnetic 
  movements 
  occurred 
  simultaneously 
  at 
  

   Haldde 
  and 
  Potsdam, 
  Prof. 
  Birkeland 
  concludes, 
  p. 
  14, 
  from 
  a 
  

   comparison 
  of 
  the 
  more 
  notable 
  large 
  disturbances 
  observed 
  at 
  

   Haldde 
  with 
  those 
  recorded 
  on 
  the 
  same 
  days 
  at 
  a 
  number 
  of 
  

   observatories 
  (including 
  Pawlowsk, 
  Copenhagen, 
  Pare 
  St. 
  Maur, 
  

   Greenwich, 
  and 
  Toronto), 
  that 
  there 
  was 
  not 
  absolute 
  identity 
  in 
  

   the 
  times 
  of 
  occurrence, 
  but 
  that 
  on 
  the 
  contrary 
  there 
  was 
  a 
  distinct, 
  

   retardation 
  of 
  phase 
  in 
  westerly 
  as 
  compared 
  to 
  easterly 
  stations. 
  

   The 
  magnetic 
  curves 
  on 
  which 
  this 
  conclusion 
  is 
  based 
  appear 
  in 
  

   Plates 
  in. 
  to 
  vn. 
  If 
  confirmed 
  as 
  a 
  general 
  fact, 
  this 
  would 
  be 
  

   very 
  important, 
  but 
  meantime 
  it 
  should 
  be 
  borne 
  in 
  mind 
  that 
  no 
  

   such 
  phenomenon 
  seems 
  to 
  have 
  been 
  detected 
  by 
  either 
  W. 
  Gr. 
  

   Adams 
  or 
  Ellis, 
  who 
  made 
  independent 
  and 
  more 
  comprehensive 
  

   investigations 
  of 
  this 
  kind. 
  

  

  Pp. 
  15 
  to 
  38 
  are 
  devoted 
  mainly 
  to 
  the 
  cause 
  of 
  magnetic 
  

   disturbances, 
  which 
  Prof. 
  Birkeland 
  believes 
  to 
  be 
  mainly, 
  if 
  not 
  

   exclusively, 
  electrical 
  currents 
  in 
  the 
  upper 
  atmosphere. 
  On 
  this 
  

   hypothesis 
  he 
  investigates 
  the 
  position, 
  direction, 
  and 
  to 
  some 
  

   extent 
  the 
  intensity 
  of 
  the 
  currents 
  to 
  which 
  may 
  be 
  ascribed 
  

   the 
  magnetic 
  disturbances 
  observed 
  at 
  Haldde, 
  and 
  also 
  those 
  

   recorded 
  at 
  various 
  stations 
  during 
  the 
  international 
  polar 
  year 
  

  

  