﻿JUNE 
  4, 
  1922 
  proceedings: 
  PHILOSOPHICAL 
  SOCIETY 
  269 
  

  

  those 
  which 
  occurred 
  during 
  the 
  period, 
  x-Vugust 
  29 
  to 
  Sept. 
  4, 
  1859; 
  in 
  

   this 
  latter 
  case, 
  northern 
  Hghts 
  were 
  visible 
  as 
  low 
  as 
  18° 
  north. 
  The 
  mag- 
  

   netic 
  disturbances 
  for 
  the 
  latter 
  period 
  were 
  of 
  almost 
  unexampled 
  size 
  

   and 
  rapidity, 
  the 
  accompanying 
  aurora 
  being 
  extraordinarily 
  brilliant 
  and 
  

   e. 
  m. 
  f 
  's. 
  of 
  700 
  to 
  800 
  volts 
  are 
  said 
  to 
  have 
  been 
  reached 
  on 
  telegraph 
  lines 
  

   500 
  to 
  600 
  km. 
  

  

  Since 
  Oersted's 
  discovery 
  somewhat 
  over 
  a 
  century 
  ago 
  of 
  the 
  deflection 
  of 
  

   a 
  compass 
  needle 
  by 
  an 
  electric 
  current, 
  hypotheses 
  have 
  been 
  repeatedly 
  

   advanced 
  respecting 
  the 
  earth's 
  magnetic 
  field 
  as 
  caused 
  by 
  electric 
  currents 
  

   in 
  the 
  earth's 
  crust. 
  However, 
  most 
  of 
  the 
  earth-current 
  observations 
  made 
  

   up 
  to 
  the 
  present 
  date 
  indicate 
  that 
  the 
  constant 
  part 
  of 
  the 
  observed 
  current 
  

   along 
  a 
  parallel 
  of 
  latitude 
  is 
  chiefly 
  towards 
  the 
  east, 
  instead 
  of 
  towards 
  the 
  

   west, 
  as 
  would 
  be 
  necessary 
  to 
  account 
  for 
  the 
  observed 
  phenomena 
  of 
  the 
  

   magnetic 
  needle. 
  

  

  At 
  the 
  International 
  Electric 
  Congress, 
  held 
  in 
  Paris 
  in 
  1881, 
  such 
  in- 
  

   terest 
  was 
  aroused 
  that 
  systematic 
  investigation 
  of 
  earth 
  currents, 
  es- 
  

   pecially 
  as 
  observed 
  in 
  telegraph 
  lines, 
  was 
  undertaken 
  in 
  various 
  countries. 
  

   This 
  material 
  was 
  furnished 
  for 
  Weinstein's 
  well-known 
  publication 
  in 
  which 
  

   data 
  obtained 
  on 
  two 
  telegraph 
  lines 
  (Berlin 
  to 
  Thorn 
  and 
  Berlin 
  to 
  Dresden) 
  

   from 
  1884 
  to 
  1887, 
  were 
  successfully 
  utilized. 
  

  

  Unfortunately, 
  the 
  interest 
  then 
  aroused 
  has 
  waned 
  and, 
  as 
  far 
  as 
  known, 
  

   there 
  is 
  at 
  present 
  only 
  one 
  observatory 
  where 
  systematic 
  earth 
  current 
  ob- 
  

   servations 
  are 
  being 
  made, 
  namely, 
  at 
  the 
  Observatorio 
  del 
  Ebro, 
  Tortosa, 
  

   Spain, 
  where 
  the 
  series 
  of 
  observations 
  began 
  in 
  1910. 
  The 
  speaker 
  proposes 
  

   to 
  arouse 
  renewed 
  interest 
  in 
  this 
  important 
  subject 
  at 
  the 
  forthcoming 
  

   Rome 
  meeting 
  of 
  the 
  International 
  Geodetic 
  and 
  Geophysical 
  Union. 
  

  

  The 
  Department 
  of 
  Terrestrial 
  Magnetism 
  is 
  planning 
  to 
  install 
  earth- 
  

   current 
  lines 
  for 
  systematic 
  observations 
  at 
  its 
  magnetic 
  observatories. 
  

   This 
  year, 
  it 
  is 
  hoped 
  that 
  such 
  lines 
  may 
  be 
  installed 
  at 
  the 
  Department's 
  

   Observatory 
  at 
  Watheroo, 
  Western 
  Australia. 
  Various 
  initial 
  investigations 
  

   have 
  been 
  in 
  progress 
  at 
  the 
  Department's 
  Laboratory 
  and 
  Dr. 
  Mauchly 
  made 
  

   a 
  report 
  to 
  our 
  Society 
  some 
  years 
  ago. 
  To 
  Mr. 
  O. 
  H. 
  Gish, 
  appointed 
  re- 
  

   cently 
  as 
  Associate 
  Physicist 
  of 
  the 
  Department, 
  has 
  been 
  assigned 
  the 
  

   continuation 
  of 
  these 
  investigations. 
  Furthermore, 
  in 
  order 
  to 
  take 
  ad- 
  

   vantage 
  of 
  the 
  experience 
  in 
  such 
  work 
  gained 
  at 
  the 
  observatory 
  in 
  Spain 
  

   and 
  to 
  ascertain 
  the 
  direction 
  in 
  which 
  further 
  study 
  is 
  desirable, 
  a 
  discus- 
  

   sion 
  of 
  the 
  eleven-year 
  series 
  at 
  the 
  observatory 
  mentioned 
  was 
  undertaken 
  

   under 
  the 
  direction 
  of 
  the 
  speaker. 
  

  

  Slides 
  were 
  shown 
  exhibiting 
  the 
  relations 
  between 
  variations 
  of 
  earth- 
  

   currents, 
  especially 
  of 
  the 
  diurnal 
  variations, 
  and 
  solar 
  activity 
  during 
  the 
  

   eleven 
  years 
  cycle. 
  The 
  relations 
  between 
  the 
  diurnal 
  variations 
  of 
  earth- 
  

   currents 
  and 
  those 
  of 
  the 
  earth's 
  magnetic 
  elements 
  were 
  also 
  briefly 
  discussed. 
  

   It 
  would 
  appear 
  that 
  the 
  relations 
  are 
  of 
  a 
  rather 
  complicated 
  character. 
  

  

  863d 
  meeting 
  

  

  The 
  863d 
  meeting 
  was 
  held 
  at 
  the 
  Cosmos 
  Club 
  March 
  11, 
  1922, 
  with 
  

   President 
  Crittenden 
  in 
  the 
  chair 
  and 
  70 
  persons 
  present. 
  

  

  William 
  Bowie: 
  The 
  yielding 
  of 
  the 
  earth' 
  s 
  crust 
  (iDustrated) 
  . 
  It 
  was 
  dis- 
  

   cussed 
  by 
  Messrs. 
  Washington 
  and 
  Hayford. 
  

  

  (Author's 
  abstract.) 
  The 
  theory 
  of 
  isostasy 
  postulates 
  that 
  blocks 
  of 
  the 
  

   crust 
  of 
  the 
  earth 
  are 
  in 
  equilibrium. 
  The 
  investigations 
  carried 
  on 
  by 
  the 
  

   U. 
  S. 
  Coast 
  and 
  Geodetic 
  Survey 
  and 
  the 
  Trigonometrical 
  Survey 
  of 
  India 
  

  

  