﻿HYDROLOGY 
  OF 
  NEW 
  YORK 
  135 
  

  

  The 
  temperatures 
  indicated 
  by 
  the 
  foregoing 
  formula 
  (31) 
  are 
  

   above 
  the 
  freezing 
  point. 
  For 
  temperatures 
  below 
  the 
  freezing 
  

   point, 
  the 
  denominator 
  of 
  the 
  fraction 
  in 
  the 
  second 
  member 
  of 
  

   the 
  formula 
  should 
  be 
  1240.2 
  — 
  1\ 
  For 
  Centigrade 
  degrees, 
  the 
  

   denominator 
  of 
  the 
  fraction 
  should 
  be, 
  when 
  the 
  temperature 
  of 
  

   the 
  dry 
  bulb 
  is 
  aibove 
  the 
  freezing 
  point, 
  610 
  — 
  £', 
  and 
  when 
  the 
  

   temperature 
  of 
  the 
  wet 
  bulb 
  is 
  below 
  the 
  freezing 
  point, 
  the 
  bulb 
  

   being 
  covered 
  by 
  a 
  film 
  of 
  ice, 
  the 
  denominator 
  should 
  be 
  689 
  — 
  t'. 
  1 
  

  

  There 
  is 
  no 
  difference 
  between 
  evaporation 
  from 
  a 
  water 
  surface 
  

   and 
  evaporation 
  from 
  land, 
  except 
  that 
  on 
  a 
  water 
  surface 
  it 
  goes 
  

   on 
  continuously, 
  while 
  on 
  land 
  evaporation 
  may 
  be 
  interrupted 
  

   from 
  lack 
  of 
  something 
  to 
  evaporate. 
  The 
  preceding 
  formul? 
  

   shows 
  that 
  the 
  force 
  of 
  vapor 
  is 
  dependent 
  upon 
  the 
  difference 
  of 
  

   the 
  dry 
  and 
  wet 
  bulb 
  thermometers, 
  and 
  not 
  in 
  any 
  degree 
  upoii 
  

   the 
  mean 
  annual 
  temperature. 
  

  

  Evaporation 
  relations. 
  Prof. 
  Cleveland 
  Abbe 
  2 
  gives 
  the 
  follow- 
  

   ing 
  relations 
  of 
  evaporation, 
  as 
  established 
  by 
  Prof. 
  Thomas 
  Tate 
  : 
  

  

  a) 
  Other 
  things 
  being 
  the 
  same, 
  the 
  rate 
  of 
  evaporation 
  is 
  

   nearly 
  proportional 
  to 
  the 
  difference 
  of 
  the 
  temperatures 
  indi- 
  

   cated 
  by 
  the 
  wet-bulb 
  and 
  dry-bulb 
  thermometers. 
  

  

  b) 
  Other 
  things 
  being 
  the 
  same, 
  the 
  augmentation 
  of 
  evapora- 
  

   tion 
  due 
  to 
  air 
  in 
  motion 
  is 
  nearly 
  proportional 
  to 
  the 
  velocity 
  of 
  

   the 
  wind. 
  

  

  c) 
  Other 
  things 
  being 
  the 
  same, 
  the 
  evaporation 
  is 
  nearly 
  in- 
  

   versely 
  proportional 
  to 
  the 
  pressure 
  of 
  the 
  atmosphere. 
  

  

  'In 
  the 
  original 
  discussion 
  of 
  this 
  matter, 
  in 
  paper 
  on 
  Relation 
  of 
  Rain- 
  

   fall 
  to 
  Runoff, 
  there 
  is 
  an 
  error 
  of 
  statement 
  in 
  formula 
  (31). 
  The 
  de- 
  

   nominator 
  of 
  the 
  second 
  member 
  should 
  be 
  1130 
  — 
  t', 
  instead 
  of 
  689 
  — 
  1\ 
  

   The 
  former 
  expression 
  is 
  for 
  Fahrenheit 
  degrees, 
  while 
  the 
  latter 
  is 
  for 
  

   Centigrade 
  degrees, 
  and 
  with 
  the 
  bulb 
  covered 
  by 
  a 
  film 
  of 
  ice. 
  

  

  In 
  formula 
  (30), 
  it 
  will 
  be 
  noted 
  that 
  Mr. 
  FitzGerald 
  makes 
  V 
  the 
  maxi- 
  

   mum 
  force 
  of 
  vapor 
  in 
  inches 
  of 
  mercury 
  corresponding 
  to 
  the 
  temperature 
  

   of 
  the 
  water. 
  Recent 
  study 
  of 
  this 
  matter 
  indicates 
  that 
  there 
  is 
  considerable 
  

   doubt 
  whether 
  formula 
  (31) 
  strictly 
  applies 
  in 
  the 
  computation 
  of 
  V, 
  but 
  

   since 
  for 
  present 
  purposes 
  an 
  illustration 
  of 
  the 
  matter 
  is 
  all 
  that 
  is 
  needed, 
  

   it 
  is 
  not 
  attempted 
  to 
  settle 
  these 
  difficult 
  questions 
  in 
  physics 
  here. 
  

  

  "Preparatory 
  Studies 
  for 
  Deductive 
  Methods 
  in 
  Storm 
  and 
  Weather 
  Pre- 
  

   dictions, 
  by 
  Prof. 
  Cleveland 
  Abbe 
  : 
  Ann. 
  Rept. 
  Chief 
  Signal 
  Officer 
  for 
  1889, 
  

   Part 
  I, 
  Appendix 
  15. 
  

  

  