492 
THE  ADMIRALTY  ASTEOXOMICAL  EXPERDIEYT 
merit  of  the  “altitude”  of  twilight  very  difficult,  when  not  far  removed  from  the  time  of 
the  sun’s  appearance. 
Considering  the  Irmar  phenomenon  again  with  the  solar,  the  cone,  if  it  had  been  the 
moon’s  zodiacal  light,  ought  to  have  appeared  before  and  not  after  the  first  fonnation 
of  the  twilight  arch ; and  it  ought  to  have  been  some  hundreds  of  times  fainter  than 
when  it  so  appeared,  as  the  lunar  representative  of  the  intensely  hrilhant  pink  blush 
preceding  the  solar  day ; and  yet,  as  such,  it  was  not  much  more  than  barely  ’sisible. 
What  then  must  be  the  almost  inconceivable  faintness  of  the  lunar  zodiacal  hght.  if  it 
exists  in  the  manner  explained  on  the  terrestrial  hypothesis,  and  how  many  grades  must 
it  be  below  invisibility  to  all  ordinary  human  vision  1 
Another  remark  recent  theories  appear  to  require.  Even  when  holding  the  heho- 
centric  nature  of  the  zodiacal  light,  some  authors  speak  of  it  as  a “ nng,''  with  a large 
interstitial  space  between  it  and  the  sun.  The  "siew  fr-om  Alta  Vista  was  as  favom-able 
as  any  observer  ever  had  for  detecting  traces  of  a ring  form,  contradistinguished  to  the 
more  generally  received  opinion  of  a lenticular  mass  gradually  increasing  in  density 
towards  the  centre,  where  the  sun  himself  is  placed ; and  I looked  particulaiiy  to  the 
subject,  as  one  bearing  immediately  on  the  recently  published  dynamic  theory  of  the 
solar  light  and  heat.  The  invariable  result  was,  that  not  the  smallest  appearance  of  any 
traces  of  the  ring  form  could  be  made  out,  but  that  every  thing  indicated  a mass  con- 
stantly increasing  in  density  towards  the  sun.  Down  to  the  very  horizon,  for  instance, 
the  intensity  of  glow  continually  increased  in  the  axis.  This  appearance,  I may  add,  is 
also  fully  borne  testimony  to  in  the  diagrams  of  the  Rev.  G.  Joxes. 
These  diagrams  merit  a more  particular  notice,  not  only  because  they  ai’e  the  largest 
printed  contribution  to  our  knowledge  of  the  zodiacal  light  yet  made,  but  because  the 
author  has  deduced  from  them  new  conclusions  as  to  the  natiu’e  of  the  phenomenon. 
The  particulars  form  the  third  volume  of  the  ‘ United  States  Japan  Expedition,’  and  it 
contains  more  than  700  quarto  pages,  of  which  one-half  are  engraved  plates.  Mr.  Joxes 
appears  to  be  an  honest,  zealous,  and  most  persevering  obseiwer.  “ Although,”  says  he. 
“ for  six  consecutive  months,  so  sick  as  often  to  be  unable  to  walk  or  stand  without  sup- 
port, I still  kept  to  my  work;  and  the  result,  whatever  it  may  be  worth,  has  the  merit  of  one 
uniform  judgment  trained  by  some  experience,  and  stimulated,  I know,  by  deep  earnest- 
ness in  the  cause.”  His  eye,  too,  must  be  powerful  beyond  the  average  of  men,  for  he 
says,  “ I could,  in  clear  nights,  with  the  naked  eye,  easily  make  out  stars  of  the  6 th,  and  I 
sometimes  thought  of  the  7th  magnitude,  through  its  (the  zodiacal  light’s)  densest  parts.” 
In  fact,  while  reading  the  introduction  to  the  volume,  I found  everything  to  admire, 
until  on  page  xi  came  this  paragraph : — “ There  is  no  mention  made  in  any  books  on  the  i 
zodiacal  hght,  of  any  differences  in  the  light  itself ; but  I very  soon  began  to  notice  that  : 
there  was  a stronger  light  at  the  central  part,  or  along  the  axis : while,  beyond  this,  on  i 
either  side,  and  also  above,  a dimmer  kind  of  light  extended  itself,  as  if  the  matter  gfring  j 
us  this  light  was  more  condensed  at  its  central  parts,  and  Avas  thinned  out  beyond.”  j 
I cannot  but  wholly  dissent  from  the  opinion  expressed  aboA  e as  to  the  publications  I 
