﻿290 
  

  

  A]SrXUAL 
  REPOET 
  SMITHSONIAN 
  INSTITUTION, 
  192 
  9 
  

  

  Nautical 
  Miles 
  

  

  20 
  30 
  

  

  jFathoms 
  

  

  Stream 
  becomes 
  shallower 
  as 
  it 
  goes 
  seaward. 
  At 
  its 
  head, 
  as 
  shown 
  in 
  

   Figure 
  2, 
  the 
  stream 
  shows 
  depths 
  of 
  a 
  thousand 
  fathoms 
  or 
  more; 
  

   but 
  the 
  depths 
  gradually 
  decrease, 
  and 
  when 
  the 
  channel 
  approaches 
  

   the 
  sea 
  the 
  greatest 
  depth 
  is 
  but 
  little 
  more 
  than 
  400 
  fathoms. 
  

  

  Nautical 
  charts 
  are 
  issued 
  primarily 
  for 
  the 
  mariner, 
  to 
  whom 
  the 
  

   shoal 
  areas 
  are 
  critical. 
  Hence 
  in 
  hydrographic 
  surveys, 
  as 
  a 
  rule, 
  

   shoal 
  areas 
  are 
  much 
  more 
  closely 
  developed 
  than 
  areas 
  of 
  deep 
  water. 
  

   So 
  that 
  it 
  may 
  be 
  assumed 
  that 
  the 
  relief 
  of 
  the 
  bottom 
  of 
  the 
  Straits 
  

   of 
  Florida 
  is 
  indicated 
  only 
  in 
  its 
  larger 
  features 
  on 
  the 
  chart. 
  It 
  is 
  

   quite 
  likely 
  that 
  a 
  detailed 
  hydrographic 
  survey 
  of 
  the 
  straits 
  would 
  

   bring 
  out 
  interesting 
  local 
  features 
  that 
  now 
  are 
  masked. 
  

  

  Throughout 
  the 
  whole 
  stretch 
  of 
  400 
  miles 
  shown 
  in 
  Figure 
  2, 
  

   the 
  Gulf 
  Stream 
  jQows 
  with 
  considerable 
  velocity. 
  It 
  is 
  clear, 
  how- 
  

   ever, 
  that 
  the 
  whole 
  mass 
  of 
  water 
  is 
  not 
  moving 
  with 
  a 
  uniform 
  

  

  velocity. 
  Confining 
  our 
  atten- 
  

   tion 
  for 
  the 
  present 
  to 
  the 
  velocity 
  

   of 
  the 
  current 
  at 
  the 
  surface 
  we 
  

   find 
  at 
  its 
  head, 
  say 
  abreast 
  of 
  

   Habana, 
  the 
  velocity 
  in 
  the 
  axis 
  

   of 
  the 
  stream 
  (shown 
  by 
  arrows 
  

   in 
  fig. 
  2) 
  to 
  be 
  about 
  2K 
  nautical 
  

   miles 
  per 
  hour, 
  or 
  2% 
  knots 
  on 
  

   the 
  average. 
  Seaward, 
  the 
  veloc- 
  

   ity 
  increases 
  gradually 
  as 
  the 
  

   cross-sectional 
  area 
  of 
  the 
  stream 
  

   decreases 
  until 
  abreast 
  of 
  Cape 
  

   Florida 
  the 
  velocity 
  becomes 
  

   about 
  3K 
  knots. 
  As 
  we 
  shall 
  see 
  

   later, 
  the 
  current 
  is 
  subject 
  to 
  

   variations; 
  and 
  it 
  is 
  therefore 
  to 
  

   be 
  empha,sized 
  that 
  the 
  velocities 
  given 
  above 
  are 
  approximate 
  average 
  

   or 
  normal 
  velocities. 
  

  

  With 
  regard 
  to 
  the 
  current 
  within 
  the 
  depths 
  of 
  the 
  Gulf 
  Stream 
  the 
  

   observational 
  data 
  are 
  in 
  general 
  fragmentary. 
  Pillsbury 
  during 
  his 
  

   investigation 
  carried 
  out 
  several 
  series 
  of 
  current 
  observations 
  in 
  the 
  

   Straits 
  of 
  Florida, 
  but 
  these 
  were 
  generally 
  confined 
  to 
  depths 
  less 
  than 
  

   1,000 
  feet. 
  From 
  these 
  observations 
  and 
  from 
  general 
  considerations 
  

   it 
  is 
  known 
  that 
  the 
  swiftest 
  thread 
  of 
  the 
  current 
  lies 
  in 
  the 
  axis 
  of 
  the 
  

   stream, 
  just 
  below 
  the 
  surface, 
  and 
  from 
  ere 
  the 
  velocity 
  decreases 
  

   with 
  increasing 
  depth. 
  In 
  the 
  axis 
  of 
  the 
  Gulf 
  Stream, 
  off 
  Habana, 
  

   Pillsbury 
  found 
  the 
  current 
  setting 
  easterly 
  with 
  a 
  velocity 
  of 
  a 
  knot 
  

   at 
  a 
  depth 
  of 
  130 
  fathoms. 
  

  

  Within 
  the 
  narrows 
  of 
  the 
  strait, 
  abreast 
  of 
  Cape 
  Florida, 
  the 
  

   velocity 
  distribution 
  may 
  be 
  considered 
  relatively 
  well 
  known. 
  Figure 
  

   3, 
  adapted 
  from 
  Wiist, 
  shows 
  the 
  velocity 
  distribution 
  across 
  the 
  section 
  

  

  TViE 
  GEOGR 
  REVIEW 
  

  

  Figure 
  3.— 
  Velocity 
  of 
  Gulf 
  Stream 
  within 
  Straits 
  

   of 
  Florida 
  

  

  