﻿HYDROLOGY 
  OF 
  NEW 
  YORK 
  197 
  

  

  others 
  not 
  here 
  published, 
  that 
  there 
  is 
  no 
  definite 
  relation 
  between 
  

   evaporation 
  and 
  mean 
  annual 
  temperature. 
  

  

  Exponential 
  formula. 
  On 
  fig. 
  10 
  this 
  relation 
  is 
  expressed 
  by 
  

   an 
  exponential 
  formula, 
  after 
  the 
  manner 
  proposed 
  by 
  Mr 
  Fitz- 
  

   Gerald 
  in 
  his 
  paper, 
  Flow 
  of 
  Water 
  in 
  48-inch 
  Pipes. 
  1 
  Such 
  a 
  

   curve 
  has 
  the 
  advantage 
  that 
  it 
  is 
  the 
  best 
  approximation 
  possible 
  

   to 
  obtain 
  from 
  the 
  given 
  data. 
  It 
  will 
  be 
  noticed 
  that 
  it 
  differs 
  

   slightly 
  from 
  the 
  curve 
  of 
  fig. 
  9. 
  At 
  30 
  inches 
  rainfall 
  this 
  differ- 
  

   ence 
  amounts 
  to 
  about 
  1.3 
  inches 
  of 
  runoff. 
  

  

  While 
  on 
  the 
  subject 
  of 
  exponential 
  formulas 
  it 
  may 
  be 
  re- 
  

   marked 
  that 
  their 
  chief 
  advantage 
  lies 
  in 
  the 
  possibility 
  of 
  taking 
  

   any 
  set 
  of 
  data 
  and 
  deducing 
  the 
  curve 
  which 
  best 
  suits 
  the 
  

   conditions. 
  

  

  Description 
  of 
  runoff 
  diagrams. 
  Fig. 
  11 
  is 
  a 
  runoff 
  diagram 
  of 
  

   the 
  Hudson 
  and 
  Genesee 
  rivers, 
  Hudson 
  river 
  for 
  1888-1901, 
  in- 
  

   clusive, 
  and 
  Genesee 
  river 
  for 
  1890-1898, 
  inclusive. 
  In 
  preparing 
  

   this 
  and 
  the 
  following 
  diagrams 
  it 
  is 
  considered 
  that 
  if 
  both 
  run- 
  

   off 
  and 
  precipitation 
  were 
  correctly 
  measured 
  the 
  points 
  would 
  

   fall 
  in 
  a 
  regular 
  curve 
  approximately 
  like 
  those 
  shown 
  on 
  figs. 
  9 
  

   and 
  10. 
  Such 
  diagrams 
  may 
  therefore 
  be 
  taken 
  as 
  a 
  criterion 
  of 
  

   the 
  accuracy 
  with 
  which 
  the 
  observations 
  have 
  been 
  made. 
  It 
  is 
  

   easier, 
  however, 
  to 
  measure 
  the 
  runoff 
  than 
  it 
  is 
  to 
  measure 
  the 
  

   precipitation, 
  and 
  hence 
  when 
  large 
  variation 
  occurs, 
  as 
  it 
  does 
  

   in 
  these 
  several 
  diagrams, 
  we 
  may 
  first 
  look 
  for 
  it 
  in 
  the 
  pre- 
  

   cipitation 
  records. 
  As 
  regards 
  the 
  Hudson 
  area, 
  it 
  has 
  been 
  the 
  

   writer's 
  custom 
  to 
  take 
  the 
  rainfall 
  of 
  the 
  northern 
  plateau 
  of 
  

   the 
  State 
  Weather 
  Bureau 
  as, 
  on 
  the 
  whole, 
  best 
  representing 
  the 
  

   rainfall 
  of 
  the 
  Upper 
  Hudson 
  area. 
  With 
  the 
  exception 
  of 
  the 
  

   years 
  1899 
  and 
  1900 
  the 
  points 
  all 
  fall 
  within 
  from 
  an 
  inch 
  to 
  

   an 
  inch 
  and 
  a 
  half 
  of 
  the 
  curve. 
  Those 
  two 
  years 
  have, 
  however, 
  

   been 
  computed 
  by 
  a 
  less 
  accurate 
  method 
  than 
  the 
  preceding 
  

   ones. 
  It 
  is 
  concluded, 
  therefore, 
  that 
  aside 
  from 
  1899 
  and 
  1900 
  

   the 
  curves 
  represent 
  the 
  rainfall 
  and 
  runoff 
  of 
  the 
  Hudson 
  and 
  

   Genesee 
  rivers 
  with 
  considerable 
  accuracy. 
  

  

  Fig. 
  12 
  shows 
  in 
  a 
  similar 
  manner 
  a 
  runoff 
  diagram 
  for 
  Mus- 
  

   kingum 
  river 
  from 
  1888 
  to 
  1895, 
  inclusive. 
  

  

  1 
  Trans. 
  Am. 
  Soc. 
  C. 
  E., 
  Vol. 
  XXXV, 
  p. 
  241. 
  

  

  