﻿232 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  the 
  air 
  flow 
  is 
  electrically 
  measured 
  or 
  controlled 
  and 
  with 
  refer- 
  

   ence 
  to 
  the 
  power 
  input 
  gives 
  a 
  clue 
  to 
  the 
  local 
  velocity. 
  

  

  The 
  regions 
  of 
  different 
  wind-speed 
  travel 
  in 
  the 
  turbulent 
  

   atmosphere 
  and 
  the 
  great 
  difficulty 
  is 
  to 
  anticipate 
  when 
  they 
  will 
  

   strike 
  you. 
  However, 
  there 
  are 
  also 
  places 
  where 
  they 
  can 
  be 
  

   found 
  quite 
  stationary. 
  On 
  the 
  leeward 
  side 
  of 
  a 
  blunt 
  wind 
  

   obstruction 
  there 
  is 
  a 
  dead 
  zone, 
  a 
  wake, 
  so 
  to 
  speak, 
  a 
  short 
  dis- 
  

   tance 
  adjacent 
  to 
  which 
  the 
  wind 
  may 
  blow 
  at 
  full 
  force. 
  Sea- 
  

   gulls, 
  swallows, 
  and 
  swifts 
  are 
  masters 
  of 
  the 
  art 
  of 
  soaring 
  back 
  

   and 
  forth 
  between 
  such 
  layers. 
  The 
  mechanism 
  of 
  the 
  capture 
  

   of 
  kinetic 
  energy 
  is 
  very 
  similar 
  to 
  that 
  of 
  circling 
  in 
  gusts. 
  The 
  

   bird 
  glides 
  in 
  the 
  dead 
  zone 
  toward 
  the 
  tower, 
  wall, 
  bosket, 
  or 
  

   whatever 
  forms 
  the 
  obstruction 
  to 
  the 
  wind. 
  Suddenly 
  the 
  bird 
  

   weaves 
  across 
  the 
  contour 
  line 
  of 
  the 
  dead 
  zone 
  into 
  the 
  open 
  wind 
  

   where, 
  due 
  to 
  its 
  inertia, 
  it 
  receives 
  a 
  powerful 
  lift. 
  After 
  having 
  

   made 
  enough 
  headway 
  against 
  the 
  wind, 
  it 
  circles 
  and 
  coming 
  

   down-wind 
  shoots 
  back 
  into 
  the 
  dead 
  zone, 
  where 
  the 
  tremendous 
  

   velocity 
  it 
  has 
  acquired 
  is 
  a 
  big 
  store 
  of 
  kinetic 
  energy 
  which 
  is 
  

   gradually 
  used 
  up 
  in 
  patrolling 
  for 
  food 
  until 
  it 
  becomes 
  necessary 
  

   to 
  resume 
  the 
  cycle 
  again. 
  

  

  Nobody 
  would 
  suggest 
  trying 
  to 
  duplicate 
  such 
  stunts 
  with 
  gliders, 
  

   because 
  the 
  combination 
  of 
  the 
  human 
  brain 
  — 
  hands 
  — 
  steering 
  mech- 
  

   anism 
  — 
  moment 
  of 
  inertia 
  of 
  the 
  wide-spanning 
  machine 
  is 
  very 
  much 
  

   slower 
  than 
  the 
  corresponding 
  chain 
  of 
  reaction 
  within 
  these 
  birds, 
  

   and 
  chances 
  would 
  merely 
  be 
  of 
  crashing 
  into 
  somx 
  rock. 
  However, 
  

   layers 
  of 
  different 
  wind 
  velocities 
  may 
  often 
  be 
  found 
  one 
  above 
  the 
  

   other. 
  As 
  a 
  rule 
  the 
  wind 
  higher 
  up 
  is 
  faster 
  than 
  down 
  below. 
  The 
  

   energy 
  stored 
  therein 
  can 
  be 
  caught 
  by 
  alternately 
  gliding 
  down- 
  

   wind 
  in 
  the 
  upper 
  layer, 
  descending 
  into 
  the 
  lower 
  one 
  where 
  the 
  

   relative 
  surplus 
  velocity 
  is 
  kept 
  in 
  reserve, 
  then 
  turning 
  around 
  and 
  

   pulling 
  up 
  into 
  the 
  upper 
  layer 
  again. 
  Here 
  a 
  powerful 
  inertial 
  

   lift 
  is 
  the 
  reward 
  of 
  the 
  whole 
  maneuver. 
  Vultures 
  have 
  been 
  seen 
  

   circling 
  this 
  way 
  in 
  India, 
  descending 
  and 
  ascending 
  rhythmically 
  

   in 
  inclined 
  orbits. 
  

  

  In 
  places 
  where 
  the 
  discontinuity 
  zone 
  separating 
  the 
  two 
  layers 
  

   is 
  sharp, 
  this 
  phenomenon 
  is 
  even 
  noticeable 
  on 
  regular 
  motor 
  air- 
  

   planes. 
  In 
  the 
  Karst 
  Mountain 
  range 
  behind 
  the 
  east 
  coast 
  of 
  the 
  

   Adriatic 
  Sea 
  sometimes 
  a 
  peculiar 
  meteorological 
  condition 
  occurs. 
  

   A 
  strong 
  uniform 
  westerly 
  warm 
  wind, 
  called 
  sirocco, 
  sweeps 
  in 
  from 
  

   the 
  sea 
  at 
  the 
  higher 
  altitude. 
  Cold 
  air, 
  called 
  bora, 
  rushes 
  down 
  the 
  

   slopes 
  of 
  the 
  bare 
  mountains, 
  mainly 
  from 
  an 
  easterly 
  or 
  north- 
  

   easterly 
  quadrant. 
  Wind-speed 
  drops 
  as 
  sudden 
  as 
  60 
  feet 
  per 
  second 
  

   west 
  against 
  15 
  feet 
  per 
  second 
  northeast 
  can 
  be 
  encountered 
  in 
  pass- 
  

   ing 
  down 
  from 
  the 
  2,800-foot 
  level 
  to 
  about 
  2,000 
  feet. 
  Flying 
  there, 
  

  

  