﻿470 
  G. 
  C. 
  Comstock. 
  — 
  The 
  Secular 
  Variation 
  of 
  Latitudes. 
  

  

  Art. 
  LI. 
  — 
  The 
  Secular 
  Variation 
  of 
  Latitudes; 
  by 
  George 
  

   C. 
  Comstock. 
  

  

  [Read 
  at 
  the 
  Washington 
  Meeting 
  of 
  the 
  American 
  Association 
  for 
  the 
  Advance- 
  

   ment 
  of 
  Science.] 
  

  

  A 
  possible 
  secular 
  change 
  in 
  the 
  position 
  of 
  the 
  terrestrial 
  

   pole 
  has 
  long 
  been 
  a 
  subject 
  of 
  discussion 
  among 
  astronomers 
  

   and 
  physicists, 
  and 
  the 
  history 
  of 
  investigations 
  made 
  in 
  this 
  

   connection 
  resembles 
  in 
  many 
  respects 
  that 
  of 
  similar 
  researches 
  

   upon 
  stellar 
  parallaxes. 
  The 
  early 
  investigators 
  expected 
  to 
  

   find, 
  and 
  announced 
  the 
  actual 
  discovery 
  of, 
  very 
  sensible 
  varia- 
  

   tions 
  of 
  both 
  kinds 
  while 
  their 
  successors 
  overturned 
  their 
  

   conclusions 
  and 
  traced 
  their 
  results 
  back 
  to 
  errors 
  of 
  observa- 
  

   tion. 
  Less 
  than 
  a 
  decade 
  ago 
  a 
  vigorous 
  interest 
  in 
  the 
  matter 
  

   of 
  latitudes 
  seemed 
  to 
  be 
  aroused 
  by 
  Fergola. 
  A 
  plan 
  for 
  

   systematic 
  research 
  was 
  proposed 
  and 
  adopted 
  and 
  for 
  a 
  time 
  

   we 
  appeared 
  to 
  be 
  on 
  the 
  eve 
  of 
  a 
  repetition 
  of 
  the 
  brilliant 
  

   success 
  attained 
  by 
  Bessel 
  and 
  Struve 
  a 
  half 
  century 
  ago 
  in 
  

   the 
  determination 
  of 
  parallaxes. 
  But 
  Fergola's 
  plan 
  seems 
  to 
  

   have 
  been 
  abandoned 
  without 
  a 
  trial 
  and 
  so 
  far 
  as 
  astronomers 
  

   are 
  concerned 
  these 
  investigations 
  have 
  fallen 
  into 
  abeyance. 
  

  

  But 
  an 
  urgent 
  demand 
  for 
  further 
  research 
  comes 
  now 
  from 
  

   another 
  quarter. 
  The 
  geologists 
  having 
  tried 
  one 
  by 
  one 
  the 
  

   various 
  hypotheses 
  which 
  have 
  been 
  advanced 
  to 
  account 
  for 
  

   the 
  glacial 
  periods 
  have 
  found 
  them 
  successively 
  inadequate 
  

   and 
  untenable. 
  In 
  the 
  inelegant 
  but 
  expressive 
  language 
  of 
  

   one 
  of 
  these 
  gentlemen 
  they 
  are 
  " 
  in 
  a 
  hole," 
  and 
  the 
  only 
  

   escape 
  from 
  the 
  difficulty 
  seems 
  to 
  be 
  through 
  the 
  assumption 
  

   that 
  the 
  terrestrial 
  pole 
  has 
  wandered 
  widely 
  from 
  its 
  present 
  

   position 
  during 
  recent 
  geologic 
  time. 
  

  

  I 
  am 
  no 
  geologist, 
  but 
  since 
  my 
  attention 
  was 
  especially 
  

   directed 
  to 
  the 
  problem 
  in 
  hand 
  by 
  geologists, 
  let 
  me 
  briefly 
  

   summarize 
  the 
  case 
  from 
  their 
  standpoint. 
  The 
  phenomena 
  

   of 
  erosion 
  indicate 
  that 
  the 
  last 
  glacial 
  epoch 
  is 
  separated 
  from 
  

   us 
  in 
  time 
  by 
  a 
  period 
  which 
  is 
  to 
  be 
  measured 
  by 
  thousands 
  

   of 
  years 
  and 
  probably 
  not 
  a 
  very 
  great 
  number 
  of 
  thousands. 
  

   At 
  that 
  epoch 
  a 
  certain 
  portion 
  of 
  the 
  earth's 
  surface, 
  includ- 
  

   ing 
  parts 
  at 
  least 
  of 
  Europe 
  and 
  North 
  America, 
  was 
  buried 
  

   in 
  ice 
  much 
  as 
  the 
  continent 
  of 
  Greenland 
  is 
  now 
  covered 
  by 
  

   an 
  almost 
  continuous 
  glacier. 
  Only 
  recently 
  has 
  the 
  area 
  cov- 
  

   ered 
  by 
  the 
  ice 
  been 
  delimited, 
  but 
  as 
  a 
  result 
  of 
  surveys 
  made 
  

   during 
  the 
  past 
  five 
  or 
  six 
  years 
  it 
  appears 
  that 
  the 
  ancient 
  

   glacier 
  covered 
  a 
  region 
  approximately 
  bounded 
  by 
  a 
  small 
  

   circle 
  of 
  the 
  earth 
  whose 
  pole 
  lies 
  somewhere 
  in 
  Greenland 
  

   and 
  whose 
  angular 
  radius 
  is 
  not 
  far 
  from 
  35°, 
  i. 
  e. 
  the 
  amount 
  

  

  