﻿WHICH 
  IS 
  CONDENSED 
  ON 
  A 
  COLD 
  SURFACE. 
  301 
  

  

  city 
  of 
  it 
  was 
  regulated 
  by 
  the 
  number 
  of 
  revolutions 
  made 
  by 
  the 
  handle 
  of 
  the 
  

   instrument 
  in 
  the 
  course 
  of 
  ten 
  seconds. 
  The 
  results 
  correspond 
  respectively 
  to 
  

   5, 
  10, 
  18, 
  and 
  25 
  of 
  these 
  revolutions, 
  or 
  on 
  a 
  rough 
  estimate 
  to 
  actual 
  velocities 
  

   of 
  4-12, 
  8-24, 
  148, 
  and 
  20-6 
  feet 
  per 
  second. 
  

  

  With 
  such 
  an 
  instrument 
  it 
  was 
  difficult 
  to 
  maintain 
  a 
  rapid 
  current 
  at 
  a 
  

   uniform 
  rate, 
  and 
  hence, 
  probably, 
  the 
  reason 
  why 
  the 
  results 
  due 
  to 
  five 
  and 
  ten 
  

   revolutions 
  of 
  the 
  handle 
  are 
  less 
  discordant 
  than 
  those 
  corresponding 
  to 
  eighteen 
  

   and 
  twenty-five 
  revolutions. 
  

  

  The 
  second 
  table 
  contains 
  the 
  values 
  of 
  M= 
  7 
  - 
  — 
  „„. 
  , 
  ,„ 
  — 
  ^ 
  and 
  of 
  m=- 
  

  

  the 
  former 
  corresponding 
  to 
  the 
  experiments 
  in 
  the 
  thirteenth 
  column, 
  and 
  the 
  

   latter 
  to 
  the 
  experiments 
  in 
  the 
  fourteenth, 
  fifteenth, 
  sixteenth, 
  and 
  seventeenth 
  

   columns 
  of 
  the 
  first 
  table. 
  The 
  results 
  in 
  column 
  twelfth, 
  for 
  reasons 
  which 
  will 
  

   be 
  obvious 
  from 
  the 
  remarks 
  on 
  that 
  column, 
  are 
  omitted 
  in 
  the 
  second 
  table. 
  

  

  Taking 
  the 
  mean 
  of 
  the 
  numbers 
  in 
  each 
  column 
  of 
  this 
  table, 
  and 
  changing 
  

   the 
  unit 
  of 
  surface 
  from 
  11*8 
  to 
  100 
  square 
  inches, 
  and 
  the 
  unit 
  of 
  time 
  from 
  five 
  

   minutes 
  to 
  one 
  minute, 
  it 
  appears 
  that 
  the 
  value 
  of 
  M 
  for 
  calm 
  air 
  is 
  012, 
  and 
  

   that 
  the 
  values 
  of 
  m 
  for 
  velocities 
  of 
  4-12, 
  8*24, 
  14-8, 
  and 
  20*6 
  feet 
  per 
  second 
  are 
  

   respectively 
  18*3, 
  26-5, 
  397, 
  and 
  44-6. 
  

  

  These 
  results 
  may 
  be 
  useful 
  in 
  various 
  meteorological 
  investigations 
  ; 
  but 
  at 
  

   present 
  it 
  is 
  proposed 
  to 
  apply 
  them 
  only 
  to 
  one 
  question 
  connected 
  with 
  the 
  

   theory 
  of 
  rain. 
  

  

  The 
  admirable 
  observations 
  of 
  Professor 
  Phillips 
  and 
  Mr 
  Gray, 
  published 
  in 
  

   the 
  Reports* 
  of 
  the 
  British 
  Association, 
  shew 
  that 
  at 
  York 
  there 
  fell 
  in 
  the 
  course 
  

   of 
  three 
  years, 
  into 
  a 
  rain-gauge 
  placed 
  on 
  the 
  ground, 
  65 
  '430 
  inches 
  of 
  rain; 
  into 
  

   a 
  gauge 
  placed 
  at 
  the 
  height 
  of 
  43 
  7 
  feet, 
  52*169 
  inches 
  ; 
  and 
  into 
  a 
  gauge 
  at 
  the 
  

   height 
  of 
  213 
  feet, 
  38'972 
  inches. 
  

  

  Professor 
  Phillips 
  has 
  proposed, 
  in 
  explanation 
  of 
  these 
  anomalous 
  results, 
  

   an 
  hypothesis 
  which 
  may 
  be 
  thus 
  enunciated. 
  As 
  rain 
  falls 
  from 
  a 
  considerable 
  

   height 
  in 
  the 
  atmosphere, 
  its 
  temperature 
  is 
  less 
  than 
  that 
  of 
  the 
  dew-point 
  of 
  

   the 
  vapour 
  through 
  which 
  it 
  passes 
  in 
  the 
  course 
  of 
  its 
  descent 
  ; 
  and 
  this 
  gives 
  

   rise 
  to 
  a 
  continuous 
  deposition 
  of 
  moisture 
  on 
  the 
  surface 
  of 
  each 
  rain-drop 
  suffi- 
  

   cient, 
  in 
  the 
  aggregate, 
  to 
  account 
  for 
  the 
  difference 
  between 
  the 
  quantities 
  of 
  

   rain 
  received 
  in 
  the 
  higher 
  and 
  lower 
  gauges. 
  

  

  This 
  ingenious 
  explanation 
  has 
  been 
  so 
  ably 
  advocated 
  by 
  its 
  proposer, 
  and 
  

   by 
  other 
  highly 
  competent 
  judges, 
  that 
  it 
  is 
  not 
  without 
  hesitation 
  I 
  venture 
  to 
  

   object 
  to 
  it, 
  on 
  the 
  ground 
  that 
  the 
  rate 
  of 
  condensation 
  which 
  it 
  assumes, 
  when 
  

   compared 
  with 
  the 
  rate 
  deduced 
  from 
  experiment, 
  is 
  too 
  great. 
  

  

  I 
  shall 
  now 
  endeavour 
  to 
  offer 
  some 
  proof 
  in 
  support 
  of 
  this 
  conclusion. 
  

  

  * 
  Vol. 
  ii., 
  p. 
  401 
  ; 
  vol. 
  iii., 
  p. 
  560 
  ; 
  vol. 
  iv., 
  p. 
  171. 
  

  

  