ON  THE  PEAK  OF  TENERIFFE. 
-517 
The  dew-point  exhibits  greater  variations  still,  amounting  on  Guajara  to  34°’9  against 
9°-4  at  the  sea-level,  and  on  Alta  Vista  to  40°T  against  13°-6  at  the  lower  level  for  the 
same  period. 
These  variations  of  daily  means  exhibit  inexplicable  discordances,  in  no  small  measure 
on  account  of  so  small  a portion  of  then’  cycle,  viz.  the  year,  being  included  in  the 
observations ; and  before  coming  to  the  consideration  of  the  absolute  quantities  for  each 
day,  it  may  be  well  to  consider  the  monthly  variations. 
(3.)  Monthly  Means. 
On  taking  the  arithmetical  means,  the  results  indicated  by  the  curves  were  powerfully 
confirmed,  \iz.  that  on  the  mountain,  the  maxima  of  temperature  and  dryness  are  earlier 
than  below;  summer,  in  fact,  at  a great  height,  is  there  nearly  coincident  with  the 
solstice.  Thus  while  at  the  sea-level  the  temperature  went  on  increasing  throughout 
July,  August,  and  September,  it  was  sensibly  decreasmg  at  Guajara  in  July  and  August  ; 
and  at  Alta  Vista,  in  August  and  September,  it  was  very  rapidly  falling.  On  going 
below  the  sea-level,  or  to  the  sea-water  itself,  the  law  was  carried  on  further  still,  the 
numbers  being  as  follows : — 
1 
i 
Date. 
1 
Sea-level. 
Sea- 
water, 
tempe- 
rature 
of. 
Guajara. 
Alta  Vista. 
Barometer. 
Tempe- 
rature. 
Depression 
of 
dew-point. 
Barometer. 
Tempe- 
rature. 
Depression 
of 
dew-point. 
Barometer. 
Tempe- 
rature. 
Depression 
of 
dew-point. 
1856, July  
August  ... 
September 
inches. 
30*045 
30*036 
30-083 
73*1 
73*8 
74*9 
11*4 
11*3 
11*4 
70*9 
72-8 
74*2 
inches. 
21*918 
21*941 
62*4 
59*6 
3^9 
33*0 
inches. 
20*572 
20*500 
O 
56*4 
46-0 
O 
25*6 
23*7 
These  means  represent  the  whole  of  the  observations  made  in  each  month  at  the 
several  stations ; at  the  sea-level  they  include  nearly  the  whole  of  each  month,  but  on 
the  mountain  only  about  half  a month  each ; this  circumstance,  however,  will  not  touch 
the  great  fact  now  brought  to  light,  of  the  mean  temperature  arriving  at  its  maximum 
earlier  at  10,702  feet  than  at  8903,  and  at  8903  earlier  than  below  it. 
Over  and  above  this  effect,  the  temperature  appears  to  follow  the  law  of  decrease  with 
altitude,  but  in  an  accelerating  ratio  so  far  as  these  three  stations  would  indicate,  which 
will  be  considered  in  the  department  of  the  '■’■'peripatetic"  observations;  and  I would 
now  rather  advert  to  the  most  remarkable  feature  of  all  in  the  mountain  climate,  viz. 
the  excessive  dryness,  amounting  at  Guajara,  in  the  contrary  terms  of  humidity  (satura- 
tion=100),  to  26,  and  at  Alta  Vista  to  38,  as  the  mean  for  two  months,  against  66  at 
the  sea-level ; or,  in  terms  of  grains  of  moisture  in  a cubic  foot  of  air  equally  compressed 
in  each  case,  to  1‘5,  1'6,  and  6-2. 
Extreme  Readings. 
At  the  sea-level  the  highest  maximum  temperature  daily  mean  was  78°'8  on  Sep- 
