﻿136 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  d) 
  The 
  rate 
  of 
  evaporation 
  of 
  moisture 
  from 
  damp, 
  porous 
  sub- 
  

   stances 
  of 
  the 
  same 
  material 
  is 
  proportional 
  to 
  the 
  extent 
  of 
  the 
  

   surface 
  presented 
  to 
  the 
  air, 
  without 
  regard 
  to 
  the 
  relative 
  thick- 
  

   ness 
  of 
  the 
  substances. 
  

  

  e) 
  The 
  rate 
  of 
  evaporation 
  from 
  different 
  substances 
  mainly 
  

   depends 
  upon 
  the 
  roughness 
  of, 
  or 
  inequalities 
  on, 
  their 
  surfaces, 
  

   the 
  evaporation 
  going 
  on 
  most 
  rapidly 
  from 
  the 
  roughest 
  or 
  most 
  

   uneven 
  surfaces 
  ; 
  in 
  fact, 
  the 
  best 
  radiators 
  are 
  the 
  best 
  vaporizers 
  

   of 
  moisture. 
  

  

  f 
  ) 
  The 
  evaporation 
  from 
  equal 
  surfaces 
  composed 
  of 
  the 
  same 
  

   material 
  is 
  the 
  same, 
  or 
  very 
  nearly 
  the 
  same, 
  in 
  a 
  quiescent 
  atmos- 
  

   phere, 
  whatever 
  may 
  be 
  the 
  inclination 
  of 
  the 
  surfaces: 
  thus 
  a 
  

   horizontal 
  plate 
  with 
  its 
  damp 
  face 
  upward 
  evaporates 
  as 
  much 
  

   as 
  one 
  with 
  its 
  damp 
  face 
  downward. 
  

  

  g) 
  The 
  rate 
  of 
  evaporation 
  from 
  a 
  damp 
  surface 
  (namely, 
  a 
  

   horizontal 
  surface 
  facing 
  upward) 
  is 
  very 
  much 
  affected 
  by 
  the 
  

   elevation 
  at 
  which 
  the 
  surface 
  is 
  placed 
  above 
  the 
  ground. 
  

  

  h) 
  The 
  rate 
  of 
  evaporation 
  is 
  affected 
  by 
  the 
  radiation 
  of 
  sur- 
  

   rounding 
  bodies. 
  

  

  i) 
  The 
  diffusion 
  of 
  vapor 
  from 
  a 
  damp 
  surface 
  through 
  a 
  

   variable 
  column 
  of 
  air 
  varies 
  (approximately) 
  in 
  the 
  inverse 
  ratio 
  

   of 
  the 
  depth 
  of 
  the 
  column, 
  the 
  temperature 
  being 
  constant. 
  

  

  j) 
  The 
  amount 
  of 
  vapor 
  diffused 
  varies 
  directly 
  as 
  the 
  tension 
  

   of 
  the 
  vapor 
  at 
  a 
  given 
  temperature, 
  and 
  inversely 
  as 
  the 
  depth 
  

   of 
  the 
  column 
  of 
  air 
  through 
  which 
  the 
  vapor 
  has 
  to 
  pass. 
  

  

  k) 
  The 
  time 
  in 
  which 
  a 
  given 
  volume 
  of 
  dry 
  air 
  becomes 
  sat- 
  

   urated 
  with 
  vapor, 
  or 
  saturated 
  within 
  a 
  given 
  percentage, 
  is 
  

   nearly 
  independent 
  of 
  the 
  temperature 
  if 
  the 
  source 
  of 
  vapor 
  is 
  

   constant. 
  

  

  1) 
  The 
  times 
  in 
  which 
  different 
  volumes 
  of 
  dry 
  air 
  become 
  sat- 
  

   urated 
  with 
  watery 
  vapor, 
  or 
  saturated 
  within 
  a 
  given 
  per 
  cent, 
  

   are 
  nearly 
  proportional 
  to 
  the 
  volumes. 
  

  

  m) 
  The 
  vapor 
  already 
  formed 
  diffuses 
  itself 
  in 
  the 
  atmosphere 
  

   much 
  more 
  rapidly 
  than 
  it 
  is 
  formed 
  from 
  the 
  surface 
  of 
  the 
  

   water. 
  (This 
  assumes, 
  of 
  course, 
  that 
  there 
  are 
  no 
  convection 
  

   currents 
  of 
  air 
  to 
  affect 
  the 
  evaporation 
  or 
  the 
  diffusion.) 
  

  

  Effect 
  of 
  wind 
  and 
  other 
  meteorological 
  elements. 
  That 
  the 
  

   velocity 
  of 
  the 
  wind 
  must 
  have 
  a 
  very 
  material 
  effect 
  upon 
  evap- 
  

   oration, 
  and 
  hence 
  upon 
  the 
  runoff 
  of 
  streams, 
  is 
  at 
  once 
  apparent 
  

   on 
  inspection 
  of 
  Mr 
  FitzGerald's 
  evaporation 
  formula, 
  given 
  in 
  a 
  

   preceding 
  section. 
  Again, 
  on 
  examining 
  the 
  annual 
  summaries 
  

  

  