ON  THE  PEAK  OF  TENEEIFFE. 
52  9 
to  clear  Alta  Vista  by  about  300  feet,  and  at  8 p.m.  the  depression  of  the  dew-point 
was  1°-1. 
On  the  16th  the  barometer  had  risen  to  20‘632,  the  temperature  increased  from  39°, 
its  lowest,  to  43°;  and  the  depression  of  the  dew-point  to  5°*3. 
During  these  days,  and  until  the  19th,  when  we  left  the  mountain,  the  sky  was  con- 
tinually cloudy,  i.  e.  there  was  a stratum  of  cloud  at  a height  greater  than  12,000  feet, 
in  addition  to  the  lower  stratum  at  4000  feet,  and  this  upper  bed  was  eminently  hazy 
and  misty.  The  sun  by  day,  and  the  moon  by  night,  were  seen  as  pale  and  watery  as 
they  are  in  the  generahty  of  English  weather ; the  autumn  had  in  fact  set  in  on  the 
mountain  top,  and  that  locality  had  lost  its  specialities  as  a site  for  astronomical 
observations. 
On  descending  the  mountain,  beyond  the  N.E.  cloud  being  broken  up  and  scattered, 
we  found  that  no  perceptible  change  in  the  weather  had  been  experienced  below.  On 
the  night  of  the  14th,  when  we  on  the  mountain  were  fearing  that  the  station  at  Alta 
Vista  would  be  undermined  or  be  washed  away  by  the  torrents  of  rain,  not  a drop  had 
fallen  on  either  the  N.  or  S.  coast  of  the  island ; nay,  even  a party  of  visitors  who  had 
left  us  at  about  3 p.m.  on  that  day,  after  the  hail-storm,  gained  the  bottom  of  the 
mountain  without  any  more  wet;  and  on  referring  to  the  Captain’s  journal  on  board 
the  yacht,  some  of  the  warmest  weather  of  the  whole  season  occurred  with  him,  when 
we  were  at  the  wettest  and  coldest  on  the  mountain. 
The  storm  then,  which,  with  all  its  accompaniments,  we  are  justified,  by  the  con- 
tinual degradation  of  temperature  going  on  during  the  whole  period  of  our  tenure  of 
Alta  Vista,  in  considering  as  the  commencement  of  autumn,  was  confined  to  the  upper 
regions  of  the  atmosphere  and  the  mountain  top,  not  descending  probably  below  9000 
feet  of  elevation.  This  circumstance  in  itself,  viewed  as  part  of  a general  law,  will 
cause  a different  rate  of  decrease  of  the  heat  of  the  atmosphere  with  altitude,  at  different 
seasons  of  the  year ; for,  in  September  for  instance,  we  should  be  stepping  from  summer 
below  to  autumn  above ; and  the  actual  difference  found,  will  be  further  increased,  if 
there  be  an  upper  stratum  of  cloud  to  reffect  back  the  heat  of  the  sun,  in  the  same 
manner  as  the  lower  stratum  was  found  to  do  in  our  meteorological  journeys.  There 
was,  too,  such  an  upper  stratum  on  September  14th  and  following  days;  and  it  appeared 
also  to  produce  the  lowering  of  the  temperature  above  described,  as  well  as  the  lessen- 
ing of  the  depression  of  the  dew-point.  As  all  these  matters  are  so  intimately  con- 
nected with  the  theory  of  refractions  and  of  barometrical  altitudes,  I subjoin  a list  of 
daily  differences  of  mean  temperature  at  the  sea-level,  and  at  the  height  of  10,702  feet 
as  observed : — 
4 A 2 
