490 
THE  ADMIEALTY  ASTEOXOmCAE  EXPEEDIEXT 
altitude,  but  not  at  the  earlier  periods,  when  the  light  was  far  too  diffuse  and  uncertain 
as  to  its  boundaries. 
(7.)  Zodiacal  Light. 
At  Guajara  the  zodiacal  light  was  observable  both  east  and  west:  at  Alta  Vista  only 
in  the  east,  on  account  of  obstructions  in  the  horizon  westward.  Xotices  of  observations 
of  this  phenomenon  will  be  found  in  the  Astronomical  Journal  under  dates  of  July  23. 
26,  30,  31,  and  August  2,  7,  8,  12,  18,  and  September  2,  4,  5,  6,  and  7.  The  objects 
proposed  were,  in  the  first  place,  to  measure  the  place  of  the  apex  of  the  light;  its 
length,  breadth,  and  shape,  and  its  angle  with  the  horizon ; and  in  the  second  place,  to 
note  any  additional  circumstances  that  could  be  made  out  bearing  on  recent  theories. 
In  the  western  direction  the  appearance  was  very  faint,  but  it  was  certainly  real ; and 
of  three  observations  taken  about  half  an  hour  after  sunset  on  July  26  and  30,  and 
August  18,  we  have  the  following  mean  quantities: — 
For  August  4th,  at  17^ 
sidereal  time 
Length  from  horizon 
Angles  of  inclination  to  horizon 
Apex  in  vH  13'’  26'"  and  D — 10'^ 
Length  from  sun 
50 
31 
i of  the  Wav. 
. Degree  of  brightness  .... 
The  greatest  probable  error  of  any  of  these  observations,  including  all  causes,  natural 
as  well  as  personal,  may  be  +6°,  and  within  such  hmits,  and  not  to  those  of  the  last 
degree  given,  we  may  assume  that  the  plane  of  the  light  is  shoym  to  be  nearly  coincident 
with  the  ecliptic. 
In  the  eastern  dhection,  the  Guajara  observations  on  July  31,  August  2,  8.  and  12. 
give,  for  the  mean  date  of  August  5,  at  O''  50'"  sidereal  time, — 
Length  from  horizon  .... 
Breadth  of  base 
Angle  with  horizon  .... 
Apex  in  3'*  48'"  ^ and  D+21° 
Length  from  sun 
Brightness 
62 
24 
75 
76 
Milky  Vmy  x 2 
The  angle  of  the  ecliptic  with  the  horizon  at  the  same  time  being  70°. 
At  Alta  Vista,  observations  obtained  on  September  2,  5,  and  7,  give  for  the  mean  date 
September  5 at  3'*  sidereal  time — 
Length  from  horizon .... 
Breadth  of  base 
Angle  with  horizon  .... 
Apex  in  /B,  5'*  20'"  and  D+17° 
Length  from  sun 
Brightness 
The  angle  of  the  ecliptic  with  the  horizon  being  78°. 
63 
27 
79 
84 
Milky  Way  X 3 
