ON  THE  PEAK  OF  TENEEIFFE. 
467 
grapher  to  the  Admiralty,  Captain  Washington.  (9.)  Double  Sextant.  By  Admiral 
Beechey.  (10.)  Polarization  apparatus.  By  the  Bev.  Baden  Powell.  (11.)  Plane 
speculum  and  apparatus  to  facilitate  the  observation  of  red  prominences  round  the  sun. 
By  J.  Nasmyth,  C.E.  (12.)  Eyepieces  and  adaptations  to  Equatorial.  By  T.  Cooke, 
Esq.,  of  York.  (13.)  Lastly,  by  Bobeet  Stephenson,  Esq.,  M.P.,  was  made  the  loan  of 
his  yacht  ‘ Titania’  of  140  tons,  and  with  a crew  of  sixteen  men,  for  the  voyage  out  and 
home,  and  during  the  whole  period  of  the  experiment. 
In  addition  to  the  above  instruments,  I took  from  the  Edinburgh  Observatory  the 
5-foot  equatorial,  presented  some  years  since  by  the  late  Bev.  B.  Sheepshanks  ; and  re- 
ceived much  kind  assistance  from  Admirals  Mannees  and  W.  H.  Smyth,  Sir  David 
Beewstee,  Mr.  Welsh  of  Kew,  and  J.  J.  Foeeestee,  Esq. ; while  in  their  official  capacities. 
Lord  Claeendon,  J.  Mueeay,  the  British  Consul  in  Santa  Cruz,  and  A.  Goodall,  acting 
Vice-Consul  in  Orotava,  rendered  important  services ; and  I have  to  mention  with  thanks 
my  obligations  to  the  Spanish  authorities,  to  L.  Hamilton,  Esq.,  C.  Smith,  Esq.,  Don 
Feancisco  Aguilae,  Don  Maetin  Bodeiguez,  Mr.  Andeew  Caepentee,  and  Herr  Keeitz, 
all  of  Teneriffe ; as  w^ell  as  to  the  Brazilian  Steam  Packet  Company. 
(2.)  Instructions  and  Suggestions. 
The  leading  object  given  to  me  was,  as  afready  stated,  to  ascertain  how  much  astrono- 
mical observation  can  be  benefited  by  raising  telescopes  high  into  the  air,  and  so  enabling 
an  observer  to  look  at  the  celestial  bodies  through  a less  depth  of  atmosphere  than 
they  could  from  any  of  the  ordinary  observatories,  established  as  they  are,  at  or  near  the 
level  of  the  sea. 
If  we  could  rise  high  enough  above  the  clouds,  not  only  should  we  at  once  have  clear 
in  place  of  cloudy  skies, — no  mean  advantage  in  itself,  as  enabling  us  to  increase  the 
number  of  observations, — but  their  quahty,  a matter  of  far  higher  importance,  would  be 
advanced  at  the  same  time.  For  in  proportion  as  the  atmosphere  itself  is  overpassed, 
so  are  the  irregularities  in  its  action  on  rays  of  light  passing  through  it ; and  these 
irregularities  are  precisely  what  form  the  chief  bar  to  accuracy  of  instrumental  measure, 
and  to  certainty  of  telescopic  vision. 
On  the  other  hand  exist  the  drawbacks,  that  on  a high  mountain  it  may  be  difficult  to 
drag  up  the  largest  class  of  telescope,  and  impossible  to  build  a large  observatory ; and 
though  the  air  be  thin  and  transparent,  it  may  be  in  such  a state  of  motion  as  to  be 
prejudicial  to  the  steadiness  of  instruments ; or  again,  the  mountain  top  may  be  always 
enveloped  in  a local  cloud.  The  exact  value  of  these  objections  was  only  to  be  found 
by  actual  trial ; and  that,  if  they  should  be  overcome,  a new  gateway  would  be  opened 
up  in  the  paths  of  science,  not  astronomical  only,  but  of  many  allied  subjects,  may  be 
gathered  from  the  very  important  mass  of  suggestions  sent  into  the  Admiralty  by  their 
several  referees,  as  below.  They  show  indeed,  what  might  be  expected  from  a good 
mountain  station,  well  worked  for  a series  of  years,  rather  than  what  a preliminary  experi- 
mental trial  on  a small  scale  would  be  able  to  accomplish  in  a few  weeks. 
