﻿322 
  0. 
  L. 
  Fasslg 
  — 
  March 
  Weather 
  in 
  the 
  United 
  States. 
  

  

  the 
  area 
  of 
  high 
  pressure, 
  usually 
  over 
  the 
  Azores, 
  throughout 
  

   the 
  year, 
  was 
  during 
  this 
  month 
  over 
  France 
  and 
  neighboring 
  

   regions 
  ; 
  during 
  a 
  portion 
  of 
  January 
  the 
  area 
  had 
  resumed 
  its 
  

   normal 
  position 
  ; 
  again 
  during 
  February 
  it 
  was 
  found 
  over 
  

   France. 
  The 
  normal 
  distribution 
  of 
  pressure 
  during 
  the 
  

   winter 
  months 
  gives 
  to 
  France 
  a 
  mild 
  climate 
  with 
  prevailing 
  

   southwesterly 
  winds. 
  During 
  the 
  presence 
  over 
  France 
  of 
  the 
  

   area 
  of 
  high 
  pressure, 
  however, 
  in 
  December 
  and 
  February 
  

   some 
  of 
  the 
  lowest 
  temperatures 
  experienced 
  during 
  the 
  

   present 
  century 
  occurred 
  ; 
  the 
  prevailing 
  winds 
  were 
  northerly 
  

   and 
  much 
  of 
  the 
  precipitation 
  was 
  in 
  the 
  form 
  of 
  snow 
  and 
  

   not 
  in 
  the 
  usual 
  form, 
  of 
  rain. 
  Further 
  study 
  of 
  mean 
  pres- 
  

   sure 
  conditions 
  over 
  the 
  globe 
  for 
  a 
  long 
  series 
  of 
  years 
  led 
  

   M. 
  Teisserenc 
  de 
  Bort 
  to 
  define 
  and 
  classify 
  the 
  different 
  maxi- 
  

   mum 
  and 
  minimum 
  areas 
  of 
  pressure 
  which 
  the 
  atmosphere 
  

   presents 
  at 
  the 
  surface 
  of 
  the 
  earth. 
  These 
  areas, 
  which 
  have 
  

   a 
  certain 
  permanence 
  in 
  a 
  given 
  season 
  and 
  which 
  are 
  found 
  on 
  

   all 
  charts 
  of 
  mean 
  pressure, 
  he 
  designates 
  "great 
  centers 
  of 
  

   action 
  of 
  the 
  atmosphere." 
  Their 
  existence 
  is 
  related 
  to 
  the 
  

   position 
  of 
  the 
  great 
  centers 
  of 
  action 
  of 
  tlie 
  globe, 
  regions 
  

   which 
  either 
  by 
  their 
  physical 
  properties 
  or 
  by 
  their 
  orographic 
  

   features 
  initiate 
  the 
  great 
  centers 
  of 
  atmospheric 
  action, 
  so- 
  

   called 
  because 
  they 
  govern 
  the 
  circulation 
  of 
  the 
  winds 
  all 
  

   round 
  them. 
  These 
  centers 
  of 
  action 
  vary 
  considerably 
  from 
  

   year 
  to 
  year, 
  during 
  the 
  same 
  month, 
  in 
  position 
  and 
  in 
  extent. 
  

   Their 
  motion 
  is 
  not 
  a 
  regularly 
  progressive 
  movement 
  in 
  the 
  

   well-defined 
  direction 
  made 
  familiar 
  to 
  us 
  in 
  the 
  study 
  of 
  the 
  

   transient 
  highs 
  and 
  lows 
  of 
  our 
  daily 
  weather 
  map, 
  but 
  is 
  

   irregular, 
  a 
  shifting 
  from 
  place 
  to 
  place 
  — 
  now 
  to 
  the 
  north 
  or 
  

   south, 
  then 
  to 
  the 
  east 
  or 
  west, 
  of 
  an 
  average 
  position 
  — 
  follow- 
  

   ing 
  no 
  law 
  at 
  present 
  recognizable. 
  It 
  was 
  shown 
  that 
  the 
  

   character 
  of 
  a 
  season 
  is 
  well 
  defined 
  when 
  it 
  is 
  known 
  what 
  

   types 
  of 
  isobars 
  prevail. 
  Two 
  important 
  principles 
  have 
  

   been 
  formulated 
  by 
  M. 
  Teisserenc 
  de 
  Bort 
  as 
  a 
  result 
  of 
  these 
  

   studies 
  ; 
  

  

  1. 
  When 
  a 
  region 
  of 
  a 
  certain 
  extent 
  shows 
  an 
  excess 
  of 
  

   temperature 
  either 
  absolute 
  or 
  relative 
  to 
  the 
  temperature 
  of 
  

   other 
  points 
  in 
  the 
  same 
  latitude, 
  there 
  is 
  a 
  tendency 
  to 
  the 
  

   formation 
  of 
  a 
  minimum 
  in 
  that 
  region, 
  and 
  an 
  almost 
  exact 
  

   coincidence 
  between 
  the 
  barometric 
  minimum 
  and 
  the 
  maxi- 
  

   mum 
  of 
  temperature 
  ; 
  moreover 
  there 
  is 
  a 
  certain 
  proportion- 
  

   ality 
  between 
  them. 
  This 
  tendency 
  is 
  shown 
  either 
  by 
  the 
  

   existence 
  of 
  a 
  closed 
  minimum, 
  or 
  by 
  an 
  inflection 
  of 
  the 
  

   isobars. 
  

  

  2. 
  Areas 
  of 
  maximum 
  pressure 
  have 
  a 
  tendency 
  to 
  form 
  in 
  

   the 
  neighborhood 
  of 
  regions 
  where 
  the 
  temperature 
  is 
  low, 
  

   either 
  absolutely 
  or 
  relatively 
  to 
  their 
  latitude. 
  

  

  