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THE  ADMTRALTT  ASTEONOmCAIi  EXPEEDIEXT 
tember  16,  and  the  lowest  71°‘0  on  July  17.  At  Guajara  65°'2  on  July  28,  and  55°’5 
on  August  4.  At  Alta  Vista  58°‘5  on  August  23,  and  38°-8  on  September  15.  Again, 
the  greatest  maximum  mean  daily  depression  of  the  dew-point  at  the  sea-level  was  19®’ 6 
on  August  27,  and  the  minimum  6°’0  on  August  29.  At  Guajara  51°’2  on  July  17, 
and  16°*3  on  August  4.  At  Alta  Vista  40°’l  on  September  12,  and  0°’0  on  September 
15.  To  this  we  may  add  as  examples  of  atmospheric  dryness,  that  among  the  isolated 
observations  on  Guajara,  the  amount  of  depression  of  the  dew-point  was  5 8°- 5 on  July  17, 
the  temperature  being  51®’5 ; which  gives  only  0*4  grain  of  water  in  a cubic  foot  of  air, 
and  a humidity  of  no  more  than  10,  while  at  the  sea-level  for  the  same  instant  it  was  62. 
(4.)  Winds. 
In  the  journals,  at  the  sea-level  and  on  the  mountain,  the  velocity  of  the  wind  was 
entered  in  miles  per  hour  by  estimation.  Guajara  station,  being  quite  on  the  top  of  the 
mountain  there,  and  undominated  by  any  neighbouring  points,  was  favourable  for 
getting  the  true  direction  of  the  wind.  Alta  Vista,  on  the  contrary,  being  on  the 
eastern  slope  of  the  Peak,  was  faulty  as  a site ; and  generally,  by  day,  in  normal  weather, 
there  was  an  east  wind  blowing  up  from  the  plain,  and  by  night  a west  wind  blowing 
down  from  the  Peak. 
Taking  means  rudely  of  the  directions  and  strength  of  the  wind  as  obseiwed  at  each 
place,  an  approximate  mean  velocity  and  direction  of  the  wind  on  each  day  has  been 
obtained,  and  has  been  entered  in  Plate  XXXVII.  for  the  period  to  which  it  refers. 
From  these  quantities,  taking  the  mean  of  all  the  days  of  corresponding  observations, 
we  find  that  during  thirty-four  days  at  the  sea-level,  the  mean  velocity  of  the  wind  was 
4’ 5 miles  per  hour,  while  on  Guajara  it  was  only  2-3  miles  for  the  same  time.  On  Alta 
Vista,  agam,  the  mean  velocity  during  twenty-three  days  was  3’ 3 miles  per  hour,  while 
it  was  5 ’8  miles  at  the  sea-level  for  the  same  period. 
Between  Guajara  and  the  sea  there  is  little  change  in  the  general  du'ection  of  the 
wmd,  northerly  being  in  both  places  to  southerly  as  2 to  1.  On  the  Alta  Vista,  on  the 
other  hand,  northerly  directions  were  to  southerly  only  as  I to  10,  the  old  proportion  at 
the  sea-level  still  remaining.  Moreover,  while  at  the  sea-level  about  one-twentieth  part  of 
the  whole  wind  was- from  the  east,  and  none  from  the  west,  there  was,  with  the  same 
amount  of  east  wind  at  Alta  Vista,  one-eighth  of  the  whole  from  the  west. 
(5.)  Height  of  Stations. 
The  great  length  of  time  during  which  simultaneous  meteorological  observations  Avere 
kept  up  at  either  mountain  station  and  on  board  the  yacht,  have  afforded  a good  insight 
into  the  uncertainties  still  existing  in  the  best  barometrical  formulae  for  the  determina- 
tion of  heights.  The  varying  results  from  the  means  of  successive  days  Avere  very 
difficult  to  interpret ; but  when  the  hourly  variations  were  tried,  and  found  to  exhibit  a 
fluctuation  through  upwards  of  170  feet  at  Guajara,  and  280  feet  at  Alta  Vista,  the 
temperature  of  the  upper  station  was  clearly  shoAvn  to  be  the  agent  at  fault ; and  this 
