ON  THE  PEAK  OE  TENEEIEFE. 
481 
neutral  stratum  below  the  S.W.  wind,  which  appears  there  to  be  always  the  direction  of 
the  upper  current  in  the  atmosphere,  in  the  summer  at  least,  for  which  season  alone  my 
descriptions  are  intended  to  apply. 
The  height  of  this  neutral  region  would  seem  to  vary  much ; sometimes  it  was  below, 
but  much  more  generally  above  9000  feet.  Hence  we  had  more  N.E.  wind  than  S.W. 
at  Guajara ; but  being  in  the  neighbourhood  of  the  neutral  stratum,  neither  wind  was 
felt  in  great  force,  except  on  one  occasion,  when  for  several  hours  in  the  morning  the 
N.E.  wind  blew  with  a velocity  of  from  twenty  to  thirty  miles  per  hour. 
This  circumstance  in  itself  confii’med  the  conclusion  already  drawn  from  the  number 
of  days  that  each  wind  was  felt,  viz.  that  we  were  much  nearer  the  N.E.  than  the  S.W. 
current.  And  finding  that  in  proportion  as  the  former  (N.E.)  predominated,  so  did  faint 
dusty  impurities  in  the  an,  and  bad  definition,  we  proceeded  to  establish  a second  sta- 
tion at  “ Alta- Vista,”  at  the  height  of  10,700  feet.  Our  earlier  experiences  on  moving 
there  confirmed  the  truth  of  the  idea,  for  there  was  on  the  whole  less  wind  than  at  Gua- 
jara, and  it  was  more  evenly  balanced  between  the  two  directions.  Our  later  expe- 
riences at  that  station  included  the  setting  in  of  autumn,  which  broke  in  upon  all  the 
regularity  of  the  summer  weather,  and  need  not  here  be  alluded  to  further,  as  our  expe- 
riment was  only  intended  to  utilize  the  summer  season. 
With  wind  then  we  were  ■visited  but  moderately,  and  we  were  equally  fortunate  with 
regard  to  fog  or  mountain  clouds;  for  though  they  existed  below  and  appeared  daily, 
dense,  closely  packed  together,  and  rolling  upon  each  other,  they  showed  no  tendency  to 
rise  higher  than  4500  feet.  With  this  depression  of  the  mountain  cloud,  including 
cumulus,  cumulostratus,  and  nimbus  below  us,  we  had  but  the  thinner  forms  of  cloud, 
cinais,  cirrocumulus,  and  some  cirrostratus,  ever  at  any  time  fioating  above  us,  or  inter- 
fering with  the  \iew  of  the  heavens.  These  only  appeared  about  once  in  five  days  in 
any  considerable  quantity. 
A more  important  quality  of  the  atmosphere  was  caused  by  the  dust-haze,  which  was 
ever  more  or  less  present,  though  sometimes  in  vastly  greater  quantities  than  at  others, 
and  was  precisely  that  which  injured,  or  rendered  impossible,  daylight  observations  of 
stars.  Where  this  dust-haze  came  from  or  went  to  we  could  never  tell ; but,  when 
present,  we  could  easily  distinguish  its  banks,  or  strata,  as  they  stretched  away  and  con- 
densed in  perspective  towards  the  horizon.  There  were  often  several  strata,  one  above 
the  other,  and  mutually  separated  by  very  clear  and  sharply-defined  spaces  of  atmo- 
sphere. When,  as  was  sometimes  the  case,  the  summits  of  Grand  Canary,  or  of  Palma, 
rising  high  above  the  sea  of  clouds,  pierced  also  these  upper  strata  of  dust-haze,  we  had, 
from  Guajara,  the  curious  phenomenon  of  zones  of  blue  mountain  alternately  distinct 
and  again  indistinct  almost  to  invisibility,  and  yet  no  cloud  or  other  recognized  impurity 
of  the  atmosphere  inteiwened. 
Being  above  much  of  this  dust,  though  perhaps  not  the  greater  part  of  it,  we  were 
evidently  better  off  than  an  obseiwer  at  the  level  of  the  sea,  when  pointing  to  a zenith 
object ; but  for  a horizontal  one  we  were  worse  off,  from  often  being  m,  and  then  look- 
3 s 2 
