ox  THE  PEAK  OF  TENEEIFFE. 
495 
The  same  result  follows  from  all  my  trials  with  the  Sheepshanks  telescope  at  Guajara, 
and  the  Pattinson  equatorial  at  Alta  Vista.  At  both  stations  Saturn  was  frequently 
observed  near  the  eastern  horizon  shortly  before  sunrise,  and  was  invariably  found  steady 
and  well-defined,  remarkably  so,  considering  the  circumstances. 
No  case  of  mirage,  in  the  sense  of  violent  disturbance  of  refraction,  arising  from 
grand  natiu’al  causes,  was  ever  seen  by  us  on  the  mountain ; and  an  exhibition  of  the 
sort  is  hardly  to  be  expected  in  a breezy  locality,  almost  isolated  in  the  upper  regions 
of  the  atmosphere.  So  that  when  Baron  Humboldt  mentions,  that  fluctuations  amongst 
the  eastern  stars  were  seen  by  Prince  Adalbeet  of  Prussia,  on  the  occasion  of  his  ascend- 
ing the  Peak,  and  standing  on  the  very  site  of  his  own  remarkable  observation,  viz.  the 
Ice  cavern,  one  is  inclined  to  ask,  if  either  of  those  observers  eliminated  from  what  he 
saw,  the  effects  of  a vent  of  hot  volcanic  air  in  that  immediate  neighbourhood  1 
On  my  first  visit  to  the  Ice  cavern,  when  standing  outside  in  the  day  time  at  the  usual 
resting-place,  my  attention  was  called  by  Mr.  Caepextee,  son  of  the  Vice-Consul,  to  the 
apparent  fumes  of  hot  ah’  distorting  the  rocks,  not  far  off,  in  the  E.N.E.  direction  from 
where  we  stood : and  we  clearly  established,  on  subsequent  visits,  that  the  place  must 
be  a passage  for  volcanic  action. 
A correction  then  for  these  heated  breaths,  as  a local  disturbing  cause,  is  essential  to 
any  observations  of  stars  made,  in  their  direction,  from  the  “Ice  cavern;”  and  while  there 
is  no  evidence  of  the  correction  having  been  applied  by  either  party,  I am  bound  to  add, 
after  ha\ing  had  my  attention  dii-ected  officially  to  the  matter, — that  there  are  several 
grave  inconsistencies  in  the  accompanying  parts  of  the  narrative  of  the  world-famous 
traveller,  which  sensibly  detract  from  the  importance  of  the  case  he  has  described. 
CHAPTER  IV. 
PHYSICAL  OBSEEVATIONS. 
(I.)  Badiation  of  the  Sun  hy  Thermometers. 
Towards  obtaining  the  radiation  of  the  sun,  we  were  kindly  lent  by  Mr.  Aiet  two 
large  black-bulb  thermometers,  having  their  bulbs  enclosed  in  glass  bells,  and  these  fur- 
nished each  with  a syringe  for  the  purpose  of  extracting  the  air.  This  part  having  been 
got  to  work  very  fairly,  the  instruments  were  used  against  each  other,  with  the  idea  of 
one  giving  the  true  temperature  of  radiation,  the  other  the  temperature  of  shade.  Each 
thermometer  rested  in  its  own  packing  box,  placed  on  a short  board ; so  that  it  might  be 
conveniently  tilted  against  a wall,  to  an  angle  of  90°  Avith  the  incident  solar  rays,  and 
was  as  much  protected  from  the  wind  as  possible.  The  lid  of  the  radiation  box  was  of 
course  always  open,  while  that  of  the  shade  box  was  closed,  except  when  the  reading 
was  being  made ; and  to  obtain  this  with  the  greatest  safety,  the  lid  was  sawed  in  two, 
so  that  the  part  covering  the  bulb  neAm  had  to  be  opened  at  all ; while  to  guard  against 
the  radiation  penetrating  through  the  lid,  two  boards  were  screwed  to  its  upper  surface 
MDCCCLVIII.  3 u 
