﻿HYDROLOGY 
  OP 
  NEW 
  YORK 
  137 
  

  

  in 
  the 
  report 
  of 
  the 
  Chief 
  of 
  the 
  Weather 
  Bureau 
  the 
  average 
  yearly 
  

   velocity 
  of 
  wind 
  is 
  found 
  to 
  vary 
  from 
  about 
  3 
  miles 
  to 
  16 
  or 
  18 
  

   miles. 
  With 
  other 
  conditions 
  the 
  same, 
  evaporation 
  will 
  be 
  much 
  

   larger 
  with 
  a 
  higher 
  wind 
  velocity. 
  

  

  The 
  preceding 
  summary 
  of 
  evaporation 
  relations 
  further 
  shows 
  

   that 
  evaporation 
  will 
  vary 
  in 
  some 
  degree 
  in 
  proportion 
  to 
  

   pressure, 
  temperature, 
  moisture 
  — 
  which 
  may 
  be 
  taken 
  to 
  include 
  

   dewpoint, 
  relative 
  humidity, 
  vapor 
  pressure, 
  precipitation, 
  and 
  

   cloudiness 
  — 
  and, 
  finally, 
  in 
  proportion 
  to 
  average 
  velocity 
  of 
  the 
  

   wind. 
  It 
  may 
  also 
  be 
  expected 
  to 
  vary 
  in 
  some 
  degree 
  in 
  propor- 
  

   tion 
  to 
  electrical 
  phenomena 
  — 
  thunderstorms, 
  auroras, 
  etc. 
  — 
  tout 
  

   as 
  yet 
  we 
  know 
  so 
  little 
  about 
  these 
  that 
  they 
  can 
  be 
  no 
  more 
  

   than 
  mentioned. 
  The 
  writer, 
  however, 
  believes 
  that 
  studies 
  in 
  the 
  

   direction 
  here 
  indicated 
  would 
  be 
  very 
  prolific 
  of 
  results. 
  For 
  

   this 
  purpose 
  two 
  or 
  three 
  stations, 
  observing 
  all 
  the 
  elements 
  

   herein 
  enumerated, 
  should 
  be 
  established 
  in 
  each 
  catchment 
  area. 
  

  

  In 
  the 
  present 
  study 
  an 
  attempt 
  has 
  been 
  made 
  to 
  correlate 
  

   these 
  elements 
  with 
  the 
  runoff, 
  but, 
  aside 
  from 
  the 
  rainfall, 
  the 
  

   data 
  are 
  too 
  indefinite 
  for 
  satisfactory 
  results. 
  It 
  is 
  for 
  these 
  

   reasons, 
  with 
  others, 
  that 
  the 
  writer 
  is 
  able 
  to 
  give 
  only 
  tentative 
  

   conclusions 
  in 
  regard 
  to 
  the 
  relation 
  of 
  rainfall 
  to 
  the 
  runoff 
  of 
  

   streams. 
  

  

  Persistency 
  of 
  evaporation. 
  The 
  persistency 
  of 
  the 
  amount 
  of 
  

   evaporation 
  for 
  any 
  given 
  stream 
  at 
  about 
  the 
  same 
  figure 
  through 
  

   long 
  periods 
  of 
  time 
  was 
  first 
  pointed 
  out 
  by 
  Messrs. 
  Lawes, 
  Gil- 
  

   bert, 
  and 
  Warrington 
  in 
  their 
  classical 
  paper 
  On 
  the 
  Amount 
  and 
  

   Composition 
  of 
  Rain 
  and 
  Drainage 
  Waters 
  Collected 
  at 
  Rothamp- 
  

   sted, 
  published 
  in 
  the 
  Journal 
  of 
  the 
  Royal 
  Agricultural 
  Society 
  

   of 
  England 
  for 
  1881. 
  As 
  to 
  why 
  evaporation 
  exhibits 
  such 
  per- 
  

   sistency 
  these 
  distinguished 
  authors 
  consider 
  it 
  largely 
  due 
  to 
  the 
  

   fact 
  that 
  the 
  two 
  principal 
  conditions 
  which 
  determine 
  large 
  

   evaporation 
  — 
  namely, 
  excessive 
  heat 
  and 
  abundant 
  rain 
  — 
  very 
  

   rarely 
  occur 
  together. 
  The 
  result 
  is, 
  specially 
  in 
  the 
  English 
  

   climate, 
  a 
  balance 
  of 
  conditions 
  unfavorable 
  to 
  large 
  evaporation. 
  

   In 
  a 
  wet 
  season, 
  when 
  the 
  soil 
  is 
  kept 
  well 
  supplied 
  with 
  water, 
  

  

  