﻿Gravity 
  to 
  Continental 
  Elevation. 
  85 
  

  

  eating 
  beyond 
  a 
  question 
  a 
  distinct 
  relation 
  between 
  the 
  devia- 
  

   tions 
  in 
  the 
  force 
  of 
  gravity 
  and 
  the 
  continental 
  elevation. 
  It 
  

   will 
  be 
  seen 
  that 
  even 
  where 
  small 
  changes 
  only 
  take 
  place 
  in 
  

   proceeding 
  from 
  point 
  to 
  point 
  they 
  are, 
  almost 
  without 
  excep- 
  

   tion, 
  in 
  the 
  same 
  direction 
  in 
  both 
  curves. 
  The 
  proper 
  inter- 
  

   pretation 
  of 
  this 
  fact 
  is 
  perhaps 
  not 
  easy. 
  In 
  the 
  formula 
  of 
  

   Bouger, 
  which 
  is 
  made 
  use 
  of 
  in 
  this 
  reduction 
  to 
  the 
  sea 
  level, 
  

   the 
  only 
  quantity 
  that 
  can 
  be 
  at 
  all 
  in 
  doubt, 
  or 
  at 
  least 
  seri- 
  

   ously 
  in 
  doubt, 
  is 
  the 
  term 
  involving 
  the 
  relative 
  density 
  of 
  the 
  

   surface 
  matter 
  to 
  that 
  of 
  the 
  earth 
  itself, 
  the 
  other 
  terms 
  refer- 
  

   ring 
  only 
  to 
  the 
  decrement 
  of 
  gravity 
  due 
  to 
  elevation. 
  It 
  might 
  

   at 
  first 
  seem, 
  therefore, 
  that 
  an 
  adjustment 
  of 
  this 
  term 
  could 
  be 
  

   made 
  which 
  would 
  harmonize 
  the 
  theoretical 
  value 
  of 
  gravity 
  

   and 
  the 
  observed 
  values 
  ; 
  that 
  is 
  to 
  say, 
  it 
  might 
  appear 
  that 
  it 
  

   would 
  be 
  only 
  necessary 
  to 
  alter 
  our 
  hypothesis 
  in 
  regard 
  to 
  

   the 
  density 
  of 
  the 
  surface 
  matter 
  of 
  the 
  earth 
  in 
  order 
  to 
  

   remove 
  the 
  discrepancies 
  that 
  are 
  shown 
  in 
  the 
  table 
  and 
  are 
  

   exhibited 
  so 
  vividly 
  in 
  the 
  diagram. 
  When 
  this 
  is 
  attempted, 
  

   however, 
  it 
  is 
  seen 
  that 
  no 
  reasonable 
  hypothesis 
  with 
  regard 
  

   to 
  the 
  density 
  of 
  the 
  continental 
  mass 
  of 
  the 
  earth 
  will 
  account 
  

   for 
  these 
  differences. 
  Indeed, 
  to 
  account 
  for 
  them 
  would 
  

   require 
  the 
  assumption 
  that 
  the 
  density 
  of 
  the 
  surface 
  matter 
  

   was 
  not 
  only 
  not 
  one-half 
  of 
  the 
  mean 
  density 
  of 
  the 
  earth, 
  

   but 
  that 
  it 
  was 
  not 
  even 
  so 
  much 
  as 
  one-third 
  of 
  the 
  mean 
  

   density, 
  or 
  possibly 
  not 
  one-fourth, 
  and 
  in 
  some 
  cases, 
  indeed, 
  

   that 
  it 
  must 
  be 
  nothing 
  at 
  all, 
  so 
  that 
  it 
  is 
  difficult 
  to 
  make 
  the 
  

   hypothesis 
  accord 
  with 
  the 
  facts. 
  

  

  It 
  may 
  be 
  well 
  to 
  remark 
  that 
  the 
  studies 
  of 
  the 
  trans-conti- 
  

   nental 
  system 
  of 
  triangulation, 
  which 
  is 
  now 
  nearly 
  completed 
  

   along 
  the 
  39th 
  parallel, 
  seem 
  to 
  show 
  that 
  the 
  figure 
  repre- 
  

   sented 
  by 
  Clark's 
  spheroid 
  is 
  in 
  very 
  close 
  agreement 
  with 
  the 
  

   reality 
  as 
  developed 
  by 
  this 
  scheme, 
  so 
  that 
  no 
  large 
  discrepan- 
  

   cies 
  in 
  the 
  value 
  of 
  the 
  force 
  of 
  gravity 
  can 
  he 
  expected 
  to 
  

   result 
  from 
  any 
  possible 
  error 
  in 
  the 
  representation 
  of 
  the 
  

   geoid 
  by 
  this 
  figure. 
  

  

  These 
  results 
  are 
  certainly 
  of 
  much 
  interest 
  and 
  importance 
  

   to 
  geologists, 
  and 
  it 
  seems 
  that 
  they 
  may, 
  when 
  the 
  subject 
  is 
  

   sufficiently 
  thoroughly 
  investigated 
  by 
  further 
  determinations 
  

   widely 
  and 
  properly 
  distributed, 
  throw 
  considerable 
  light 
  on 
  

   the 
  internal 
  structure, 
  and 
  the 
  formation 
  of 
  that 
  part 
  of 
  the 
  

   earth 
  lying 
  nearest 
  the 
  surface. 
  They 
  evidently 
  demonstrate 
  

   the 
  great 
  value 
  and 
  scientific 
  interest 
  of 
  gravity 
  determinations, 
  

   conducted 
  as 
  skillfully 
  and 
  as 
  rapidly 
  as 
  have 
  been 
  these 
  under 
  

   the 
  direction 
  of 
  Mr. 
  Putnam. 
  

  

  In 
  connection 
  with 
  this 
  subject, 
  it 
  may 
  be 
  of 
  interest 
  to 
  add 
  

   that 
  during 
  this 
  campaign 
  a 
  number 
  of 
  comparisons 
  were 
  made 
  

   of 
  the 
  half-second 
  pendulum 
  system, 
  which 
  was 
  generally 
  used 
  

  

  