﻿1875.] 
  

  

  On 
  the 
  Reduction 
  of 
  Anemograms. 
  

  

  511 
  

  

  VIII. 
  c< 
  Reduction 
  of 
  Anemograms 
  taken 
  at 
  Armagh 
  Observatory 
  

   in 
  the 
  Years 
  1857 
  to 
  1863." 
  By 
  T. 
  R. 
  Robinson, 
  D.D., 
  F.R.S., 
  

   &c. 
  Received 
  June 
  11, 
  1875. 
  

  

  The 
  instrument 
  with 
  which 
  these 
  observations 
  were 
  made 
  is 
  described 
  

   in 
  the 
  Transactions 
  of 
  the 
  Royal 
  Irish 
  Academy, 
  vol. 
  xxii., 
  and 
  a 
  con- 
  

   tinuous 
  series 
  of 
  its 
  records 
  exist 
  from 
  1845 
  to 
  1870. 
  With 
  the 
  

   limited 
  resources 
  of 
  this 
  Observatory 
  it 
  was 
  not 
  in 
  my 
  power 
  to 
  reduce 
  

   them 
  ; 
  but 
  it 
  seemed 
  to 
  some 
  distinguished 
  members 
  of 
  the 
  Royal 
  Society 
  

   desirable 
  to 
  ascertain 
  whether 
  such 
  observations 
  are 
  competent 
  to 
  develop 
  

   any 
  laws 
  amid 
  the 
  seeming 
  lawlessness 
  of 
  the 
  winds, 
  and 
  they 
  obtained 
  

   for 
  me 
  a 
  grant 
  from 
  the 
  Government 
  Fund 
  to 
  discuss 
  the 
  anemograms 
  

   of 
  these 
  seven 
  years. 
  Unfortunately 
  the 
  work 
  has 
  been 
  long 
  delayed 
  by 
  

   various 
  accidents. 
  

  

  Of 
  the 
  causes 
  of 
  wind 
  some 
  are 
  undoubtedly 
  periodical 
  ; 
  and 
  though 
  

   they 
  are 
  masked 
  by 
  others 
  of 
  greater 
  magnitude, 
  which, 
  in 
  the 
  present 
  

   state 
  of 
  our 
  knowledge, 
  seem 
  quite 
  lawless, 
  yet 
  these 
  will 
  disappear 
  from 
  

   the 
  mean 
  of 
  a 
  sufficient 
  number 
  of 
  observations 
  and 
  leave 
  as 
  residual 
  the 
  

   first. 
  Of 
  the 
  periodical 
  causes 
  the 
  unequal 
  distribution 
  of 
  heat 
  is 
  the 
  

   most 
  important 
  • 
  and 
  this, 
  depending 
  on 
  the 
  place 
  of 
  the 
  sun, 
  is 
  evidently 
  

   a 
  function 
  of 
  the 
  time. 
  

  

  The 
  immediate 
  data 
  of 
  the 
  anemograms, 
  the 
  velocity 
  and 
  direction 
  of 
  

   the 
  wind, 
  though 
  not 
  the 
  most 
  convenient 
  for 
  combining 
  in 
  great 
  num- 
  

   bers, 
  yet 
  are 
  those 
  which 
  interest 
  most 
  directly 
  the 
  general 
  inquirer 
  ; 
  and 
  

   I 
  have 
  presented 
  them 
  in 
  a 
  Table, 
  which 
  shows 
  for 
  each 
  month 
  of 
  the 
  

   seven 
  years 
  the 
  mean 
  velocity 
  of 
  the 
  wind 
  in 
  each 
  octant, 
  the 
  number 
  

   of 
  hours 
  during 
  which 
  it 
  has 
  blown, 
  the 
  maximum 
  in 
  each 
  month, 
  the 
  

   number 
  of 
  hours 
  above 
  25 
  miles, 
  and 
  the 
  number 
  during 
  which 
  the 
  record 
  

   = 
  0. 
  The 
  most 
  striking 
  fact 
  shown 
  by 
  this 
  Table 
  is 
  its 
  extreme 
  irregu- 
  

   larity, 
  not 
  merely 
  from 
  octant 
  to 
  octant 
  or 
  month 
  to 
  month, 
  but 
  from 
  

   year 
  to 
  year. 
  Both 
  velocity 
  and 
  hours 
  are 
  a 
  maximum 
  in 
  the 
  octant 
  

   S.SW., 
  a 
  minimum 
  in 
  N.NE., 
  their 
  products 
  being 
  as 
  6 
  : 
  1. 
  As 
  to 
  

   monthly 
  variations, 
  the 
  amount 
  of 
  wind 
  is 
  a 
  maximum 
  in 
  January, 
  de- 
  

   creasing 
  to 
  July 
  in 
  the 
  ratio 
  of 
  2\ 
  : 
  1, 
  and 
  thence 
  increasing 
  to 
  the 
  end 
  

   of 
  the 
  year, 
  with 
  an 
  exception 
  in 
  the 
  case 
  of 
  March, 
  which 
  is 
  greater 
  

   than 
  February 
  as 
  1*13 
  : 
  1. 
  This, 
  however, 
  does 
  not 
  establish 
  the 
  common 
  

   idea 
  of 
  equinoctial 
  gales 
  ; 
  for 
  the 
  hours 
  above 
  25 
  miles 
  are 
  fewer 
  in 
  March 
  

   than 
  in 
  February, 
  and 
  there 
  is 
  no 
  excess 
  in 
  September 
  above 
  October. 
  

   There 
  is 
  also 
  no 
  clear 
  indication 
  of 
  any 
  influence 
  of 
  the 
  solar 
  spots 
  ; 
  but 
  

   for 
  detecting 
  this 
  several 
  decennial 
  periods 
  will 
  be 
  necessary. 
  The 
  annual 
  

   variations 
  are 
  equally 
  notable. 
  The 
  maximum 
  velocity 
  ranges 
  from 
  71 
  

   in 
  1861 
  to 
  19 
  in 
  1860. 
  If 
  the 
  mean 
  velocity 
  for 
  each 
  month 
  be 
  taken 
  

   without 
  reference 
  to 
  direction, 
  it 
  is 
  13*51 
  for 
  January, 
  4-24 
  for 
  June, 
  

   and 
  that 
  for 
  the 
  whole 
  year 
  is 
  9*73. 
  A 
  mode 
  of 
  discussion 
  which 
  seems 
  

   more 
  likely 
  to 
  give 
  definite 
  laws 
  is 
  to 
  resolve 
  each 
  velocity 
  into 
  a 
  southern 
  

  

  vol. 
  xxtii, 
  2 
  K, 
  

  

  