ON  THE  PEAK  OE  TENEEIEPE. 
469 
“ 8.  It  is  also  desirable  that  FRAUifHOFEE’s  spectral  lines  should  be  observed  with 
various  elevations  of  the  sun,  and  in  different  parts  of  the  sky,  and  should  be  compared 
with  observations  made  at  the  bottom  of  the  mountain. 
“ 9.  The  determination  of  the  comparative  horizontal  intensity  of  terrestrial  magnet- 
ism above  and  below  would  be  useful,  unless  the  magnetism  of  the  mountain  should 
vitiate  all  magnetic  observations. 
“10.  A few  observations  of  temperature  at  various  times,  radiation,  moisture,  and 
electricity,  are  to  be  recommended.  These,  like  all  those  last  mentioned,  should  be 
comparative. 
“11.  Advantage  may  be  taken  of  a residence  on  the  mountain  for  making  such  an 
examination  as  will  decide  whether  the  mountain  is  a favourable  one  for  experiments  on 
the  attraction  of  mountains.  It  will  be  borne  in  mind,  that  if  not  favourable  for  deter- 
minmg  the  attraction  north  and  south  by  means  of  the  zenith-sector,  it  may  be  favour- 
able for  determining  the  attraction  east  and  west  by  means  of  the  transit  instrument, 
provided  that  it  is  possible  to  carry  a galvanic  communication  over  the  mountain. 
“ 12.  If  the  general  tenor  of  the  observations,  which  Professor  Smyth  shall  be  able  to 
make,  leads  him  to  think  that  material  advantage  may  be  produced  to  astronomy  by  the 
establishment  at  some  future  time  of  an  observatory  of  more  permanent  character  at  a 
great  elevation,  the  mountain  may  be  examined  for  the  purpose  of  deciding  whether  it 
is  upon  the  whole  a favourable  place  for  such  an  establishment,  and  what  point  of  the 
mountain  will  prove  practically  the  best  locality. 
“13.  In  submitting  to  their  Lordships  these  drafts  of  suggestions,  I would  beg  leave 
again  to  refer  to  the  opinion  which  I have  expressed  in  article  2,  that  it  is  desirable 
that  Professor  Smyth  be  fettered  as  little  as  possible  by  instructions. 
“ I have  the  honour  to  be.  Sir, 
“ Your  very  obedient  Servant, 
(Signed)  “ G.  B.  Airy. 
“ 1856,  May  29th. 
'•^Additional  Suggestions  for  Professor  C.  P.  Smyth,  hy  G.  B.  Airy. 
“ Observations  for  the  height  and  duration  of  twilight. 
Dip  of  the  sea-horizon. 
Refractions  near  the  horizon. 
Solar  radiation.” 
II. — Letter  from  Sir  John  Herschel  to  the  Secretary  of  the  Admiralty, 
dated  Collingwood,  hth  May,  1856. 
“ Sir, — In  reply  to  your  letter  of  the  2nd  inst.,  informing  me  that  the  Lords  Com- 
missioners of  the  Admiralty  have  been  pleased  to  sanction  a grant  of  £500  to  meet  the 
