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  HYDROLOGY 
  OF 
  NEW 
  YORK 
  95 
  

  

  By 
  observing 
  the 
  relation 
  indicated 
  in 
  the 
  foregoing 
  tabula- 
  

   tions, 
  together 
  with 
  hight 
  of 
  ground 
  water, 
  one 
  may 
  approxi- 
  

   mately 
  compute 
  the 
  rainfall 
  from 
  the 
  runoff. 
  In 
  the 
  same 
  way 
  

   the 
  runoff 
  may 
  be 
  approximately 
  computed 
  from 
  the 
  rainfall. 
  

  

  Map 
  of 
  average 
  rainfall 
  in 
  the 
  State 
  of 
  New 
  York. 
  On 
  plate 
  

   XCVITI 
  of 
  the 
  Report 
  of 
  the 
  United 
  States 
  Board 
  of 
  Engineers 
  on 
  

   Deep 
  Waterways, 
  the 
  writer 
  has 
  given 
  the 
  average 
  rainfall 
  at 
  a 
  

   large 
  number 
  of 
  stations 
  throughout 
  the 
  State 
  of 
  New 
  York. 
  

   When 
  this 
  map 
  was 
  prepared 
  considerable 
  time 
  was 
  expended 
  in 
  

   drawing 
  lines 
  of 
  equal 
  rainfall 
  upon 
  it, 
  but 
  so 
  many 
  discrepan- 
  

   cies 
  appeared 
  that 
  it 
  was 
  finally 
  concluded, 
  for 
  the 
  present, 
  that 
  

   it 
  should 
  be 
  allowed 
  to 
  stand 
  without 
  such 
  lines. 
  The 
  only 
  way 
  

   these 
  contours 
  could 
  be 
  drawn 
  with 
  any 
  satisfaction 
  was 
  to 
  omit 
  

   stations 
  which 
  conflicted 
  too 
  much 
  therewith. 
  This, 
  the 
  writer 
  

   did 
  not 
  feel 
  justified 
  in 
  doing. 
  The 
  observations 
  are 
  not 
  exten- 
  

   sive 
  enough 
  to 
  enable 
  one 
  to 
  draw 
  these 
  lines. 
  

  

  Length 
  of 
  time 
  required 
  to 
  make 
  good 
  a 
  series 
  of 
  rainfall 
  records. 
  

   This 
  question 
  is 
  partially 
  answered 
  in 
  the 
  writer's 
  second 
  report 
  

   on 
  the 
  Upper 
  Hudson 
  Storage 
  Surveys, 
  for 
  1896, 
  by 
  a 
  short 
  analy- 
  

   sis 
  of 
  a 
  paper 
  by 
  Alexander 
  R. 
  Binnie, 
  Member 
  of 
  the 
  Institution 
  

   of 
  Civil 
  Engineers. 
  1 
  

  

  One 
  of 
  the 
  important 
  problems 
  worked 
  out 
  by 
  Mr 
  Binnie 
  is 
  an 
  

   answer 
  to 
  this 
  question 
  : 
  What 
  is 
  the 
  least 
  number 
  of 
  years 
  

   the 
  continuous 
  record 
  of 
  which, 
  when 
  a 
  mean 
  fall 
  has 
  been 
  deter- 
  

   mined, 
  will 
  not 
  be 
  materially 
  affected, 
  as 
  far 
  as 
  the 
  value 
  of 
  

   the 
  mean 
  is 
  concerned, 
  even 
  if 
  the 
  record 
  be 
  extended 
  by 
  a 
  greater 
  

   number 
  of 
  years 
  of 
  observation 
  ? 
  Mr 
  Binnie 
  says 
  : 
  

  

  Collaterally, 
  inquiry 
  must 
  also 
  be 
  made 
  if 
  the 
  period 
  necessary 
  

   to 
  determine 
  the 
  true 
  mean 
  fall 
  is 
  in 
  any 
  way 
  affected 
  by 
  the 
  

   amount 
  of 
  the 
  mean 
  fall 
  of 
  rain 
  ; 
  or 
  if 
  any 
  approximate 
  rule 
  can 
  

   be 
  applied 
  to 
  all 
  countries, 
  and 
  to 
  differing 
  amounts 
  of 
  mean 
  

   annual 
  rainfall 
  at 
  different 
  stations. 
  

  

  To 
  approach 
  the 
  subject 
  without 
  bias, 
  some 
  good 
  records 
  of 
  

   long 
  periods 
  must 
  be 
  carefully 
  examined, 
  and 
  it 
  must 
  be 
  found, 
  

   not 
  how 
  near 
  the 
  averages 
  of 
  the 
  shorter 
  periods 
  into 
  which 
  they 
  

  

  i 
  On 
  Mean 
  or 
  Average 
  Rainfall 
  and 
  the 
  Fluctuations 
  to 
  Which 
  it 
  is 
  Sub- 
  

   ject, 
  by 
  Alexander 
  R. 
  Binnie. 
  M. 
  Inst. 
  C. 
  E.: 
  Proc. 
  Inst 
  C. 
  E., 
  Vol. 
  CIX 
  

   11892), 
  pp. 
  89-172. 
  

  

  