The  length  of  the  camera  table  and  its  frame  is  12^  inches
over  all,  with  a  centre  aperture  in  the  frame  of  1 1  inches  by
3^  inches.
The  dark  slide  needs  no  special  description.  It  carries  a
plate  1 1  inches  by  3  inches,  this  length  of  plate  being  sufficient
to  photograph  as  much  of  the  spectrum  as  can  be  focussed  at
the  same  time,  with  sufficient  accuracy  for  good  measurement.
As  at  present  fixed,  the  spectrum  photograph  extends  from
wave-length  7000  to  about  3800  Angstrom  units.  The  focus
with  this  range  is  perfectly  good,  and  though  the  prisms  and
lenses  will  give  a  spectrum  extending  to  3100  Angstrom  units,
the  focus  has  not  been  found  to  be  sufficiently  good  for  the
whole  range,  and,  therefore,  the  ultra-violet  portion  is  excluded,
but  can  be  obtained  by  swinging  the  camera  frame  round  its
bolt,  as  described  above.
With  regard  to  the  method  of  covering  the  apparatus  in
order  to  protect  it  from  daylight,  this  is  done  by  means  of  two
thicknesses  of  satteen,  supported  by  light  wooden  laths,  which
are  fastened  to  the  upright  side  supports  on  the  lens  and  slit
tables.  The  satteen  is  nailed  down  on  each  side  of  the  quarter-
ing, after  being  stretched  tightly  over  the  laths.  A  special
arrangement,  of  cours6j  is  necessary  in  the  case  of  the  covering
of  the  camera  frame.  The  method  adopted  is  as  follows :  a
light  frame,  R,  about  15  inches  long  by  6  inches  high,  is  erected
vertically  on  the  camera  frame  about  4  inches  in  front  of  the
camera  table.  Four  laths,  S  and  T,  pass  from  the  corners  of
this  to  the  uprights  on  the  table  carrying  the  telescope  lens.
