﻿512 
  

  

  Dr. 
  T. 
  R. 
  Robinson 
  on 
  the 
  

  

  [Jnne 
  17, 
  

  

  component 
  S 
  and 
  a 
  western 
  "W, 
  to 
  deduce 
  from 
  these 
  interpolation 
  for- 
  

   mulae 
  involving 
  periodic 
  functions 
  of 
  the 
  time 
  for 
  periods 
  of 
  one 
  or 
  more 
  

   years, 
  and 
  from 
  the 
  changes 
  of 
  these 
  functions 
  in 
  successive 
  periods 
  to 
  

   derive 
  some 
  general 
  laws. 
  At 
  first 
  sight 
  this 
  might 
  seem 
  impracticable, 
  

   from 
  the 
  excessive 
  discordance 
  of 
  the 
  values 
  for 
  the 
  same 
  in 
  different 
  

   years. 
  Thus 
  in 
  the 
  first 
  term 
  of 
  the 
  set, 
  January 
  l 
  d 
  h 
  , 
  the 
  extreme 
  

   difference 
  in 
  the 
  seven 
  years 
  is, 
  for 
  "W" 
  20*89, 
  for 
  S 
  25-35. 
  Evidently 
  

   single 
  hours 
  were 
  out 
  of 
  the 
  question, 
  and 
  even 
  the 
  mean 
  for 
  the 
  seven 
  

   years, 
  as 
  was 
  evident 
  from 
  examining 
  their 
  probable 
  errors. 
  However, 
  I 
  

   meaned 
  each 
  hour 
  for 
  the 
  seven 
  years, 
  then 
  combined 
  these 
  in 
  periods 
  of 
  ten 
  

   days, 
  but 
  ultimately 
  took 
  their 
  mean 
  for 
  the 
  entire 
  month. 
  These 
  monthly 
  

   means 
  are 
  given 
  in 
  Table 
  III., 
  from 
  which 
  it 
  appears, 
  first, 
  that 
  all 
  the 
  

   ultimate 
  values 
  of 
  "W 
  and 
  S 
  are 
  positive. 
  This 
  arises 
  from 
  the 
  pre- 
  

   ponderance 
  of 
  positive 
  over 
  negative 
  values 
  ; 
  but 
  the 
  latter 
  occur 
  so 
  fre- 
  

   quently 
  that 
  they 
  evidently 
  belong 
  to 
  the 
  wind 
  system 
  ; 
  and 
  I 
  was 
  at 
  first 
  

   disposed 
  to 
  mean 
  and 
  develop 
  them 
  separately. 
  I 
  tried 
  it 
  for 
  January 
  

   and 
  June, 
  but 
  saw 
  that 
  in 
  the 
  present 
  state 
  of 
  our 
  knowledge 
  it 
  would 
  

   be 
  useless. 
  In 
  January 
  the 
  negative 
  values 
  are 
  0*27 
  of 
  the 
  whole, 
  in 
  

   June 
  0-374 
  ; 
  and 
  they 
  are 
  found 
  in 
  the 
  septennial 
  means 
  of 
  almost 
  every 
  

   hour, 
  but 
  so 
  irregularly 
  distributed 
  that 
  it 
  would 
  be 
  almost 
  impossible 
  to 
  

   develop 
  them 
  in 
  terms 
  of 
  the 
  time. 
  Even 
  were 
  this 
  done, 
  we 
  could 
  

   not 
  combine 
  in 
  any 
  particular 
  instance 
  the 
  negative 
  and 
  positive 
  results 
  

   unless 
  we 
  knew 
  the 
  causes 
  which 
  occasionally 
  mix 
  the 
  polar 
  and 
  equa- 
  

   torial 
  currents. 
  I 
  therefore 
  took 
  the 
  entire 
  means 
  as 
  alone 
  available. 
  

   Secondly, 
  that, 
  as 
  I 
  anticipated, 
  notwithstanding 
  the 
  discordance 
  of 
  the 
  

   individual 
  observations, 
  the 
  means 
  of 
  from 
  196 
  to 
  217 
  present 
  a 
  notable 
  

   agreement, 
  and 
  the 
  differences 
  which 
  they 
  exhibit 
  are 
  subject 
  to 
  law. 
  If 
  

   we 
  examine 
  the 
  vertical 
  columns 
  (which 
  give 
  the 
  hours 
  of 
  each 
  month), 
  

   we 
  find 
  in 
  each 
  a 
  principal 
  maximum 
  and 
  minimum 
  and 
  one 
  or 
  more 
  

   lesser 
  ones. 
  The 
  epochs 
  of 
  these 
  vary 
  with 
  the 
  season. 
  For 
  "W 
  in 
  winter 
  

   the 
  chief 
  maximum 
  is 
  from 
  noon 
  to 
  3 
  p.itf., 
  in 
  summer 
  from 
  9 
  A.M. 
  to 
  

   noon 
  ; 
  for 
  S 
  it 
  varies 
  less, 
  being 
  a 
  little 
  before 
  noon. 
  The 
  principal 
  

   minimum 
  occurs 
  from 
  6 
  p.m. 
  to 
  10 
  p.m., 
  both 
  for 
  "W 
  and 
  S. 
  

  

  The 
  extreme 
  diurnal 
  ranges 
  are 
  greatest 
  in 
  3Iarch, 
  2*14 
  and 
  2-40 
  ; 
  

   least 
  in 
  November, 
  0-74 
  and 
  0*79. 
  

  

  Examining 
  the 
  horizontal 
  columns, 
  which 
  give 
  the 
  monthly 
  variation, 
  the 
  

   existence 
  of 
  law 
  is 
  still 
  more 
  evident. 
  "W 
  has 
  a 
  maximum 
  in 
  January, 
  

   a 
  minimum 
  in 
  February 
  ; 
  its 
  greatest 
  maximum 
  in 
  March, 
  its 
  least 
  mini- 
  

   mum 
  in 
  April 
  ; 
  a 
  smaller 
  maximum 
  in 
  August, 
  and 
  a 
  smaller 
  minimum 
  in 
  

   November. 
  The 
  variations 
  are 
  greater 
  here 
  than 
  in 
  the 
  horary 
  columns. 
  

  

  The 
  law 
  for 
  S 
  is 
  simpler 
  : 
  it 
  has 
  one 
  maximum 
  in 
  December 
  and 
  one 
  

   minimum 
  in 
  July; 
  its 
  range, 
  too, 
  is 
  something 
  greater. 
  

  

  The 
  mean 
  W 
  for 
  the 
  whole 
  seven 
  years 
  = 
  2-4805 
  miles, 
  the 
  mean 
  S 
  = 
  

   3-8398 
  miles, 
  which 
  give 
  the 
  mean 
  V= 
  4-5713, 
  mean 
  D 
  = 
  32°54' 
  44", 
  and 
  

   the 
  actual 
  translation 
  of 
  air 
  39648 
  miles. 
  

  

  