472 
THE  ADMIEALTT  ASTEONOMICAE  EXPEEDIEXT 
sees,  I anticipate  that  this  special  object  will  be  successfully  accomplished  by 
him. 
“ 5th.  He  will  of  course  be  furnished  with  one  or  two  of  the  best  portable  telescopes 
which  England  can  furnish,  for  which  he  will  requii-e  one  or  two  tents,  especially  made 
for  the  purpose,  and  which,  with  the  sanction  of  the  Treasury,  I could  have  made  here ; 
in  addition  to  which  he  will  require  an  order  for  the  issue  of  two  marquees  or  bell-tents 
from  the  Tower,  or  some  other  military  depot,  for  himself  and  attendants,  with  a supply 
of  stretchers,  bedding,  and  cooking  utensils ; and  as  the  steamers  for  Teneriffe  start  from 
this  port,  I shall  be  happy  to  receive  them  here,  and  see  that  everything  is  properly 
provided  to  enable  the  Professor  to  carry  on  his  duties  effectually. 
“ 6th.  In  the  foregoing  observations  I have  confined  myself  to  the  special  object  which 
Professor  Smyth  had  in  view,  and  the  appliances  to  effect  it ; but  Teneriffe,  from  its  great 
altitude,  its  symmetrical  form,  its  position  on  the  confines  of  the  tropics  and  the  trade- 
winds,  is  the  most  remarkable  landmark  on  the  face  of  the  earth,  and  its  meridian  was 
long  ago  proposed  to  be  the  first  meridian  for  all  nations;  and  I should  truly  rejoice  it 
the  Government,  in  addition  to  sanctioning  the  necessary  expenditure  for  observations 
on  the  surface  of  the  heavenly  bodies,  would  also  sanction  the  necessary  expenditure  for 
observations  by  which  their  mean  density  might  be  determined  with  more  precision  than 
it  is  possible  it  could  be  on  any  other  spot  on  the  earth. 
“ 7th.  My  attention  has  been  specially  directed  to  this  pomt  of  late;  the  primary 
triangulation  of  the  Uirited  Kiirgdom  has  just  beerr  brought  to  a close,  and  fforn  it  we 
have  deduced  the  form  and  dimensions  of  the  earth.  Irr  the  autumn  of  last  year  I had 
observations  made  at  Arthur’s  Seat  near  Edinburgh,  for  the  purpose  of  determining  the 
mean  density  of  the  earth ; the  results  of  these  observatiorrs  arrd  computatiorrs  will  be 
read  at  the  Royal  Society  on  Thursday  rrext,  the  8th  first.  The  determinatiorr  of  these 
points  is  of  the  very  highest  importance  in  physics ; the  size  arrd  density  of  the  earth  are 
our  only  units  of  measure  by  which  we  cair  calculate  the  distance,  size,  and  density  of 
the  heavenly  bodies ; and  I could  not  but  feel  how  much  more  valuable  and  trustworthy 
would  the  observations  which  were  made  at  Arthrrr’s  Seat  have  beerr  if  they  had  been 
made  on  the  flarrks  of  the  Peak  of  Teneriffe. 
“ 8th.  The  Peak  of  Teneriffe  is  in  round  numbers  5000  times  greater  iir  its  rrrass  than 
Arthur’s  Seat,  and  its  attractiorr,  as  affecting  the  plumb-lirre,  carrrrot  be  irrrrch  less  than 
twenty  times  greater.  The  Peak  is  also,  from  its  form  arrd  mirreral  structirre,  pecirharly 
well-adapted  for  such  observations,  and  I feel  that  if  Her  Majesty^’s  Govenrrrrerrt  would 
sanction  the  necessary  expenditure,  there  is  no  scientific  reseai'ch  which  would  be  riewed 
with  greater  interest  by  the  whole  world. 
“ 9th.  The  command  of  so  large  a body  of  trained  observers  arrd  sm'vey^ors  as  we  have 
orr  the  Ordnance  Survey,  fortunately  errables  us  to  urrdertake  this  irrvestigation  at  no 
great  expense,  and  with  little  interruptiorr  to  the  progress  of  the  Natioiral  Sirrvey.  I 
do  not  anticipate  that  the  party  rreed  be  absent  from  Eirgland  rrrore  tlrair  forrr  rrrontlis. 
and  it  would  consist  of  not  more  than  eight  Sappers  froirr  the  Survey',  and  aboirt  twenty 
