524 
THE  ADMIEALTY  ASTEONOMICAE  EXTEETATEVT 
Engl.  feet. 
Guajara,  or  culminating  point  of  wall  of  gi'eat  crater  of  elevation  . 8.903 
Floor  of  crater  of  elevation,  generally 7,200 
Canadas,  or  outer  boundary  of  the  floor 6,900 
i’rom  this  last  level  there  is  a nearly  uniform  descent  on  the  Orotava  side,  at  an  angle 
of  about  12  degrees  to  the  sea  beach. 
The  height  of  the  Narix  entered  above,  is  derived  from  the  stunpiesometer  observa- 
tions made  half  an  hour  before  reaching,  and  three-quarters  of  an  hour  after  having 
passed  it,  on  our  slow  ascent  of  the  Peak  on  September  8.  The  instruments  were 
observed  also  at  the  Narix,  ^.  e.  within  about  ten  yards  of  the  httle  vent-hole,  out  of 
which  about  as  much  steam  was  issuing  as  a 2-mch  pipe  might  supply  from  a low- 
pressure  boiler.  As  far  as  I knew  at  the  time,  the  Narix  obsen'ations  were  equal  in 
value  to  any  that  were  made  that  day,  and  were  accordingly  computed  with  the  rest  ; 
they  gave  a height  of  11,868  feet,  or  upwards  of  100  feet  higher  than  the  next  obseiwa- 
tion-point  which  we  reached  in  our  continual  ascent  of  the  regular  slope  of  the  moun- 
tain. A difference  of  10  degrees  in  the  temperature  at  the  Narix  and  the  other  stations 
looked  at  first  like  an  error  of  observation ; but  on  referring  to  the  oiiginal  note-book, 
and  finding  that  the  increase  was  not  an  exact  ten,  and  had  been  participated  in  by  the 
thermometer  of  the  sympiesometer,  the  drj^-bulb  and  the  wet-bulb,  there  could  be  no 
doubt  of  the  observations  being  good,  and  fully  trustworthy  in  as  far  as  lay  in  them. 
The  instruments  then  may  be  considered  to  show  that  there  is  an  escape  of  volcanic 
heat  at  this  point;  and  seeing  that  the  depression  of  the  dew-point  is  somewhat  increased 
also,  we  may  look  on  the  steam  as  a consequence  rather  than  the  cause  of  this  local 
warmth.  Reducing  the  temperature  above  and  below  the  Narix  to  the  mean  for  24 
hours,  and  taking  the  mean  of  them,  46°-7  is  given  as  the  true  temperatui'e  of  the  level 
of  that  spot,  the  observed,  after  similar  correction,  being  5 7°' 5.  Similarly  with  the 
depression  of  the  dew-point,  2 8°' 7 ought  to  have  been  found,  but  the  instrument 
showed  32°' 2. 
(7.)  Meteoi'ological  Descent  and  Ascent  of  the  Mountain. 
In  descending  from  Alta  Vista  to  Orotava  on  August  25,  and  ascending  again  on 
August  30  with  the  large  equatorial,  I took  the  opportunity  of  making  careful  meteoro- 
logical observations,  placing  the  instruments  we  had  used  on  the  mountain  in  a sort  of 
portable  observatory,  or  tall  box,  fastened  on  a mule  in  such  a position  as  to  hang  nearly 
vertical ; and,  while  made  with  numerous  openings  above  and  below  and  on  the  sides,  to 
admit  of  the  circulation  of  air,  it  was  covered  outside  with  bright  tinfoil,  to  guard  against 
effects  of  solar  radiation.  The  mule  was  stopped  whenever  observations  were  to  be  made, 
or  the  wet-bulb  to  be  wetted ; and  the  results  are  as  worthy  of  confidence  as  those  made 
at  one  of  the  stationary  positions.  They  were,  however,  necessarily  loaded  with  the 
hourly  variations,  and  to  eliminate  these,  tables  of  double  entry  hav’e  been  constructed 
to  reduce  the  thermometer  and  depression  of  dew-point,  observed  at  any  instant,  to  the 
