494 
THE  ADMERALTT  ASTEOXOHICAX  EXPEEDIEXT 
sequences  of  the  zodiacal  light  medium,  on  the  heliacal  hypothesis,  vaning  in  density 
with  its  distance  from  the  sun,  as  is  ’visibly  the  case  ’with  the  hght ; for,  given  an  extreme 
rarity  in  our  neighbourhood,  and  much  greater  comparative  density,  united  with  stronger 
illumination,  in  the  neighbourhood  of  the  sun,  there  ’will  be  hardly  any  sensible  varia- 
tion in  the  apparent  phenomena  seen  about  the  sun  from  the  earth,  whether  this  be.  or 
be  not,  immersed  in  the  outermost  portions.  Some  very  slight  symptoms,  as  I have 
described  already,  were  given  at  Alta  Vista,  of  the  rare  boundaries  of  the  zodiacal  light 
exterrdirrg  beyond  the  earth’s  orbit ; and  Mr.  Joxes’s  poweriul  eye  would  doubtless  have 
showrr  them  stronger  still;  but  to  him  would  of  comse  have  been  intensified  also  the 
denser  part  within  the  orbits  of  Venus  and  Mercury;  so  that  the  question  of  the  place 
of  the  mass  of  the  light  would  remain  where  it  was. 
Towards  the  errd  of  the  American  volume,  a rrrrmber  of  cases  of  limar  zodiacal  hght 
are  given ; but  there  again  the  effects  of  lurrar  da’wn  do  not  seem  to  have  been  frrlly 
allowed  for ; and  while  feeling  the  utmost  admiration  for  the  Rev.  G.  JoxES,  as  an  horrest 
arrd  most  persevering  observer,  and  while  recommending  to  general  attention  those  phe- 
rrornena  of  lateral  and  latitude  charrge  which  he  considers  that  he  has  discovered,  still  I 
carrnot  look  orr  his  noble  volume,  but  as  in  the  light  of  a collection  of  rmreduced  astro- 
nornical  observations ; and  as  being  therefore  not  yet  altogether  arrived  at  a point,  for 
having  theoretical  views  founded  upon  it. 
(8.)  Lateral  Lefr action. 
Amongst  the  instructions  communicated  to  me  by  the  xAdmiralty  were  the  two 
following : — 
“ The  observer’s  attention  should  be  directed  to  any  instance  of  lateral  refraction  like 
that  remarkable  case  described  by  Humboldt  as  ha’ving  occm’red  to  him  at  Orotava.” 
“ Observations  to  verify  Humboldt’s  remarks  orr  the  lateral  osciQation  of  stars  near 
the  horizon.” 
These  two  passages  may  be  assumed  to  refer  to  the  pherromenon  described  at  pp.  69 
and  70  of  Bohn’s  translation  of  vol.  i.  of  Baron  Humboldt’s  celebrated  ‘ Persorral  Xarra- 
tive;’  and  alluded  to  again  in  his  still  more  celebrated  ‘ Cosmos,’  vol.  hi.  Sabine’s  trans- 
lation, pp.  55  and  56. 
Thence  it  would  appear  that,  not  from  Orotava,  but  from  the  “ Ice  caverrr,"  at  a 
height  of  11,050  feet,  on  the  Peak  of  Terreriffe,  very  shortly  after  daybreak  on  June 
22nd,  1799,  small  stars  7 and  8 degrees  high,  towards  the  E.N.E.,  appeared  to  move 
about  in  a variety  of  abnormal  ways,  to  an  exteirt  that  -was  aburrdarrtly  arrd  even 
strikingly  ’visible  to  the  naked  eye. 
The  learned  Baron  suggests  that  the  approach  of  the  suir,  still  rrrarry  degrees  belou 
the  horizon,  disturbirrg  the  layers  of  the  atmosphere,  was  the  cause  of  the  pherronrenon 
he  witnessed.  In  that  case  we  might  expect  that  the  effect  should  be  frequerrtly  and 
widely  observable.  This  is,  however,  rregatived  by  his  owir  more  numerous  South  Ame- 
ricair  observations,  as  he  himself  mentions. 
