ON  THE  PEAK  OF  TENEEIFFE. 
527 
the  depression  increases  from  10°  to  30°.  On  August  25,  however,  a rapid  diminution  is 
indicated  at  about  10,000  feet,  and  the  concomitant  circumstance  is  observed,  that  there 
is  that  day  a cloud  on  the  top  of  the  Peak  (12,000  feet  high) ; and  as  in  ascending  we 
gradually  came  underneath  the  mist,  we  were  evidently  approximating  to  the  conditions 
of  our  starting  from  the  sea-level,  with  the  3000-foot  stratum  of  cloud  above  us. 
A third  result  we  may  draw  is,  that  while  the  expected  difference  was  found  between 
the  wind  at  the  top  and  bottom  of  the  mountain,  viz.  S.W.  above  and  N.E.  below,  the 
stratum  of  cloud  was  not  found  in  the  space  between  the  two,  but  in  or  below  the 
middle  of  the  N.E.  current  of  air.  This  was  certainly  only  the  mountain  cloud,  which 
is  limited  in  horizontal  extent  to  a few  miles ; but  even  the  sea-  or  the  true  N.E.-cloud, 
which  was  far  more  extensive, — stretching,  in  fact,  as  far  as  the  eye  could  observe,  when 
many  thousand  feet  above  it, — only  reached  to  between  4000  and  5000  feet  of  elevation, 
while  the  N.E.  wind  extended  in  height  from  the  very  sea  itself  to  about  9000  feet. 
This  was  the  general  state  of  things  for  over  two  months  at  Guajara,  when  the  weather 
was  settled  in  its  N.E.  trade ; and  it  may  be  perhaps  only  when  a storm  comes  to  break 
up  the  adjustment,  that  a cloud  finds  itself  occasionally,  as  may  be  seen  about  Table 
Mountain  in  South  Africa,  between  two  opposite  currents  of  ah’,  and  made  to  spin  round 
and  round  by  their  opposing  action. 
(8.)  Electricity. 
For  upwards  of  a month,  an  electrometer  (lent  by  Mr.  Aiey)  was  observed  daily  on 
Guajara.  The  instrument  had  travelled  so  safely,  that  the  two  strips  of  gold-leaf  that 
had  been  attached  in  England,  were  found  in  good  working  order  in  Teneriffe.  The 
glass  bell,  however,  having  unfortunately  been  fixed  by  the  maker  in  a wooden  base,  the 
contraction  of  this  from  excessive  drought  at  last  broke  the  bell.  During  the  whole 
period  of  observation  by  day  and  by  night,  the  electricity  was  moderate  in  quantity,  and 
always  resinous ; this  was  during  the  season  of  the  N.E.  trade-wind,  and  within  its 
infiuence,  though  above  its  clouds.  Had  the  instrument  lasted  longer,  something  more 
varied,  if  not  more  interesting,  would  have  been  found ; for  our  subsequent  experiences 
at  Alta  Vista  introduced  us  to  a different  current  of  the  atmosphere,  and  at  last  to  a 
complete  change  of  weather;  and  on  the  vei’y  day  that  we  left,  September  19,  a heavy 
shower  of  rain  fell,  accompanied  with  a cloud  on  the  Peak,  two  or  three  hashes  of  light- 
ning, and  somewhat  loud  thunder.  This  was  the  first  electric  display  we  had  seen  since 
entering  the  region  of  the  trade-winds  on  July  5,  in  lat.  37°,  and  it  certainly  came  from 
the  S.W.  Occasionally  I had  thought  at  Guajara  that  there  were  indications  of  elec- 
tricity in  the  forms  of  the  clouds  fioating  at  a great  height  over  the  station  from  the 
S.W.;  and  on  the  night  of  August  1st  and  the  morning  of  August  2nd  (see  Meteorological 
Journal),  I watched  with  intense  interest  a large  cloud  that  remained  stationary  over 
the  mountain  for  seven  hours,  and  was  every  moment  altering  its  form,  fitfully  and 
instantaneously,  more  like  an  aurora  than  a cloud.  On  no  occasion,  however,  was  the 
electrometer  affected ; and  on  no  occasion,  indeed,  did  we  cease  to  be  under  the  domina- 
MDCCCLVIII.  4 A 
