75  VARIETIES. 
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Atmospheric  pressure  at  the  Eastern  base  of  the  Andes,  as  observed  by 
Lieut.  Herndon,  U.  S.  N. — In  1851  the  United  States  Government  sent 
Lieut.  Herndon  to  Peru,  with  directions  to  cross  the  Andes  to  the  head 
navigable  waters  of  the  Amazon  within  the  territory  of  that  Government, 
and  to  follow  them  to  the  ocean  through  the  main  stream  of  that  river,  with 
the  view  of  making  observations  on  the  climate,  productions  and  commerce 
of  the  countries  drained  by  its  upper  branches,  and  more  especially  in 
reference  to  the  navigability  of  the  latter  streams.  Having  reached  a  suitable 
point  he  launched  his  canoe,  and  after  a  variety  of  adventures  arrived  safely 
at  Para,  having  made  a  water  voyage  of  3200  miles.  After  sailing  nearly 
900  miles  down  the  Ucayle  in  a  Northern  direction  along  the  base  of  the 
mountains,  by  the  indication  of  the  boiling  point  of  water  he  had  descended 
from  1253  feet  to  126  feet  above  the  level  of  the  ocean  according  to  the  usual 
method  of  reckoning,  but  here,  to  his  surprise,  the  boiling  point  gradually 
descended  again  until  he  arrived  at  Egas,  900  miles  further,  when  it  indi- 
cated an  elevation  of  1715  feet,  after  which  it  gradually  arose  to  the  normal 
height  at  the  Atlantic  coast. 
Lieut.  Maury,  U.  S.  Navy,  in  a  communication  to  the  Academy  of  Natural 
Sciences,  Philadelphia,  remarks  in  reference  to  Lieut.  Herndon's  observa- 
tions, "  that  after  ascending  the  Andes  and  coming  down  the  Amazon  to  a 
considerable  distance  he  (apparently)  ascended  or  went  up  hill ;  now  we 
know  this  was  not  the  case,  because  he  was  all  the  time  drifting  down  the 
stream  in  a  canoe.  To  reconcile  this  apparent  paradox  between  the  incli- 
nation of  this  slope  of  the  continent,  as  shown  on  the  one  hand  by  the  run- 
ning water  of  the  river,  and  on  the  other  by  the  pressure  of  the  air,  it  is 
necessary  to  suppose  that  when  he  boiled  his  water  at  the  Eastern  base  of 
the  Andes,  he  was  in  fact  under  a  bank  of  atmosphere,  and  that  the  pressure 
under  this  bank  was  so  great  as  to  force  the  boiling  point  up  very  nearly 
to  the  sea  level." 
"  These  experiments  were  made  in  South  latitude,  and  in  the  trade  wind 
region  of  that  hemisphere.  These  winds  strike  nearly  perpendicularly 
against  the  Andes,  the  tops  of  which  range  extend  in  many  places  nearly, 
if  not  quite,  as  high  as  do  the  trade  winds  themselves.  Now,  then,  what  is 
the  effect  of  such  an  obstruction  as  the  Andes  afford  to  the  passage  of  the 
South-east  trade  winds  ?  If  we  may  judge  by  similar  obstructions  to  run- 
ning water,  we  have  no  hesitation  in  saying  that  the  effect  is  to  bank  up." 
Lieut.  Maury,  by  way  of  illustration,  alludes  to  the  effect  produced  at 
Ilurlgate,  where  the  water  is  piled  up  by  resistance  afforded  by  the  natural 
obstructions  to  the  passage  of  the  tidal  wave.   In  like  manner  he  thinks 
