﻿212 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1922. 
  

  

  and 
  so 
  on, 
  doubling 
  at 
  each 
  union. 
  Hence 
  we 
  should 
  expect 
  more 
  

   drops 
  having 
  the 
  weights 
  1, 
  2, 
  4, 
  8, 
  ... 
  . 
  than 
  any 
  intermediate 
  

   values, 
  and 
  this 
  expectation 
  has 
  been 
  fully 
  verified 
  by 
  observations 
  

   on 
  all 
  sorts 
  of 
  rains. 
  

  

  THE 
  MEASURING 
  OF 
  CLOUD 
  HEIGHTS. 
  

  

  It 
  is 
  always 
  interesting 
  and 
  sometimes 
  very 
  useful 
  to 
  know 
  the 
  

   heights 
  of 
  the 
  clouds, 
  or, 
  to 
  be 
  more 
  exact, 
  the 
  heights 
  of 
  their 
  

   bases 
  — 
  useful, 
  frequently, 
  to 
  the 
  aviator 
  to 
  whom 
  very 
  low 
  clouds 
  

   may 
  be 
  a 
  danger 
  and 
  certainly 
  a 
  nuisance, 
  and 
  useful 
  as 
  an 
  aid 
  in 
  

   forecasting 
  the 
  local 
  weather 
  for 
  the 
  next 
  few 
  hours. 
  

  

  There 
  are 
  several 
  methods 
  of 
  determining 
  the 
  heights 
  of 
  clouds 
  

   as 
  accurately 
  as 
  ever 
  is 
  necessary. 
  Indeed, 
  under 
  favorable 
  circum- 
  

   stances, 
  the 
  error 
  may 
  not 
  be 
  more 
  than 
  a 
  few 
  feet. 
  

  

  1. 
  The 
  aviator, 
  for 
  instance, 
  can 
  take 
  the 
  reading, 
  corrected 
  if 
  

   necessary, 
  of 
  his 
  altimeter 
  the 
  instant 
  he 
  climbs 
  into 
  the 
  base 
  of 
  

   a 
  cloud. 
  

  

  2. 
  A 
  pilot 
  balloon 
  (small 
  free 
  balloon 
  without 
  instruments) 
  may 
  

   be 
  observed 
  from 
  two 
  stations 
  a 
  mile, 
  say, 
  apart, 
  and 
  its 
  exact 
  direc- 
  

   tion 
  from 
  each 
  station, 
  both 
  horizontal 
  and 
  vertical, 
  noted 
  as 
  it 
  dis- 
  

   appears 
  into 
  a 
  cloud 
  base. 
  From 
  these 
  directions, 
  which 
  can 
  be 
  deter- 
  

   mined 
  very 
  accurately 
  with 
  suitable 
  theodolites, 
  and 
  from 
  the 
  known 
  

   distance 
  between 
  the 
  two 
  observing 
  stations 
  and 
  the 
  height 
  of 
  either 
  

   above 
  the 
  other, 
  the 
  cloud 
  height 
  is 
  readily 
  obtained 
  by 
  a 
  simple 
  

   trigonometrical 
  calculation. 
  

  

  3. 
  Any 
  definite 
  spot 
  on 
  the 
  base 
  of 
  a 
  cloud 
  may 
  be 
  simultane- 
  

   ously 
  observed 
  (triangulated, 
  to 
  be 
  exact) 
  from 
  two 
  stations 
  and 
  

   its 
  height 
  calculated 
  from 
  the 
  data 
  thus 
  obtained, 
  precisely 
  as 
  in 
  

   the 
  case 
  of 
  the 
  pilot 
  balloon. 
  The 
  observations, 
  of 
  course, 
  may 
  be 
  

   either 
  visual 
  or 
  photographic; 
  the 
  latter, 
  if 
  well 
  done, 
  generally 
  

   being 
  the 
  better 
  since 
  it 
  affords 
  opportunity 
  for 
  detailed 
  study 
  and 
  

   independent 
  measurements 
  on 
  many 
  different 
  points. 
  

  

  4. 
  The 
  angular 
  altitude 
  of 
  a 
  kite 
  and 
  the 
  length 
  of 
  wire 
  out, 
  at 
  

   the 
  time 
  it 
  enters 
  a 
  cloud 
  base, 
  also 
  furnish 
  a 
  fair 
  means 
  of 
  com- 
  

   puting 
  the 
  desired 
  height. 
  

  

  5. 
  The 
  exact 
  time 
  of 
  disappearance 
  of 
  a 
  kite 
  up 
  into 
  a 
  cloud 
  may 
  

   be 
  noted, 
  and 
  the 
  height 
  of 
  the 
  kite 
  at 
  that 
  instant, 
  and 
  hence 
  also 
  of 
  

   the 
  cloud, 
  determined 
  by 
  subsequent 
  examination 
  of 
  the 
  temperature 
  

   and 
  pressure 
  records 
  on 
  the 
  kite 
  instruments. 
  

  

  6. 
  The 
  level 
  of 
  storm 
  clouds, 
  or 
  low 
  clouds 
  at 
  the 
  time 
  of 
  strong 
  

   winds, 
  and 
  of 
  ordinary 
  cumuli, 
  can 
  be 
  tolerably 
  closely 
  computed 
  

   from 
  the 
  current 
  values 
  of 
  the 
  temperature 
  and 
  humidity. 
  

  

  The 
  above 
  are 
  by 
  no 
  means 
  all 
  the 
  possible 
  ways 
  of 
  measuring 
  

   the 
  heights 
  of 
  clouds, 
  but 
  they 
  are 
  the 
  more 
  accurate 
  and 
  the 
  ones 
  

   most 
  commonly 
  practiced. 
  

  

  