﻿134 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  As 
  regards 
  the 
  relation 
  between 
  mean 
  annual 
  temperature 
  and 
  

   evaporation, 
  the 
  questions 
  raised 
  by 
  Mr 
  Vermeule 
  are 
  very 
  inter- 
  

   esting 
  and 
  have 
  received 
  considerable 
  study 
  from 
  the 
  writer 
  ever 
  

   since 
  the 
  publication 
  of 
  Mr 
  Vermeule's 
  report 
  in 
  1894. 
  This 
  study 
  

   has 
  been 
  specially 
  directed 
  toward 
  determining 
  whether 
  there 
  was 
  

   any 
  way 
  of 
  showing 
  by 
  diagrams, 
  definitely, 
  that 
  any 
  such 
  relation 
  

   really 
  existed. 
  

  

  Evaporation 
  

  

  FitzGerald's 
  formula 
  for 
  evaporation. 
  We 
  may 
  consider 
  Mr 
  

   FitzGerald's 
  formula 
  for 
  evaporation, 
  1 
  which 
  is 
  

  

  E 
  

  

  ( 
  Y 
  -^)( 
  1 
  + 
  ^) 
  (30) 
  

  

  60 
  

  

  In 
  this 
  formula 
  V=the 
  maximum 
  force 
  of 
  vapor 
  in 
  inches 
  of 
  

   mercury 
  corresponding 
  to 
  the 
  temperature 
  of 
  the 
  water; 
  v=the 
  

   force 
  of 
  vapor 
  present 
  in 
  the 
  air; 
  W=the 
  velocity 
  of 
  the 
  wind 
  in 
  

   miles 
  per 
  hour; 
  and 
  E— 
  the 
  evaporation 
  in 
  inches 
  of 
  depth 
  per 
  

   hour. 
  It 
  can 
  be 
  shown 
  that 
  there 
  is 
  going 
  on 
  nearly 
  always 
  a 
  

   condensation 
  of 
  moisture 
  from 
  the 
  air 
  upon 
  any 
  water 
  surface. 
  

   At 
  the 
  same 
  time 
  there 
  is 
  going 
  on 
  a 
  loss 
  of 
  moisture 
  from 
  the 
  

   water 
  surface 
  by 
  evaporation. 
  The 
  intensity 
  of 
  both 
  these 
  opera- 
  

   tions 
  depends 
  upon 
  the 
  difference 
  in 
  temperature 
  between 
  the 
  air 
  

   and 
  any 
  water 
  surface 
  with 
  which 
  it 
  may 
  be 
  in 
  contact. 
  When 
  

   the 
  temperature 
  of 
  air 
  and 
  water 
  is 
  the 
  same, 
  theoretically 
  both 
  

   processes 
  stop. 
  Broadly, 
  evaporation 
  may 
  be 
  said 
  to 
  measure 
  the 
  

   difference 
  of 
  these 
  two 
  exchanges. 
  Wind 
  velocity 
  also 
  exerts 
  a 
  

   decided 
  effect 
  on 
  the 
  intensity 
  of 
  evaporation. 
  

  

  For 
  illustrative 
  purposes, 
  v, 
  the 
  force 
  of 
  vapor 
  present 
  in 
  the 
  air 
  

   may 
  be 
  computed 
  by 
  the 
  following 
  : 
  

  

  ' 
  ■ 
  oAm-t^ 
  h 
  

  

  1130 
  — 
  ^ 
  ; 
  

  

  In 
  which 
  t*=force 
  of 
  vapor 
  in 
  the 
  air 
  at 
  time 
  of 
  observation; 
  

   . 
  . 
  V=force 
  of 
  vapor 
  in 
  a 
  saturated 
  air 
  at 
  temperature 
  

   of 
  if\ 
  

   £— 
  temperature 
  of 
  the 
  air 
  in 
  Fahrenheit 
  degrees, 
  in- 
  

   dicated 
  by 
  the 
  dry 
  bulb 
  ; 
  

   t'— 
  temperature 
  of 
  evaporation 
  given 
  by 
  wet 
  bulb 
  ; 
  

   7i=hight 
  of 
  barometer. 
  

  

  1 
  Tranfl. 
  Am. 
  Soc. 
  C. 
  E., 
  Vol. 
  XV, 
  pp. 
  581-646. 
  

  

  