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  Scientific 
  Intelligence. 
  

  

  Campbell's 
  photographs 
  of 
  this 
  kind 
  taken 
  in 
  India 
  in 
  1898 
  are 
  

   regarded 
  as 
  the 
  finest 
  ever 
  made. 
  

  

  The 
  eclipse 
  committee 
  appointed 
  by 
  the 
  Astronomical 
  and 
  

   Astrophysical 
  Society, 
  Messrs. 
  Newcomb, 
  Hale, 
  Barnard 
  and 
  

   Campbell, 
  have 
  issued 
  a 
  circular 
  letter, 
  under 
  date 
  of 
  March 
  29, 
  

   specifying 
  in 
  eleven 
  classes 
  the 
  different 
  lines 
  of 
  work 
  that 
  may 
  be 
  

   profitably 
  undertaken, 
  offering 
  suggestions, 
  in 
  many 
  cases 
  quite 
  

   minute, 
  as 
  to 
  methods 
  of 
  work, 
  and 
  inviting 
  the 
  cooperation 
  of 
  

   all 
  who 
  intend 
  to 
  observe 
  the 
  eclipse. 
  

  

  The 
  classification 
  of 
  work 
  is 
  as 
  follows 
  : 
  

  

  (1) 
  Observations 
  both 
  direct 
  and 
  photographic 
  of 
  the 
  relative 
  

   position 
  of 
  the 
  sun 
  and 
  moon 
  for 
  correcting 
  the 
  tables. 
  

  

  (2) 
  Drawings 
  of 
  the 
  corona 
  made 
  at 
  the 
  telescope, 
  noting 
  espe- 
  

   cially 
  the 
  structural 
  features 
  near 
  large 
  prominences 
  and 
  the 
  

   general 
  outline 
  of 
  the 
  corona. 
  

  

  (3) 
  The 
  color 
  of 
  prominences. 
  

  

  (4) 
  Photographs 
  of 
  the 
  corona. 
  

  

  Attention 
  is 
  called 
  to 
  three 
  classes 
  of 
  camera 
  lenses 
  which 
  may 
  

   be 
  used 
  for 
  special 
  purposes 
  : 
  

  

  (a) 
  Those 
  of 
  focal 
  length 
  about 
  six 
  times 
  the 
  aperture 
  with 
  a 
  

   wide 
  range 
  of 
  exposure, 
  from 
  j^- 
  up 
  to 
  20 
  seconds, 
  for 
  recording 
  

   the 
  outer 
  corona 
  and 
  extensions. 
  

  

  (b) 
  Those 
  of 
  focal 
  length 
  about 
  fifteen 
  times 
  the 
  aperture 
  with 
  

   exposures 
  from 
  Jg 
  to 
  2 
  seconds, 
  for 
  recording 
  the 
  mid 
  corona, 
  

   inner 
  corona 
  and 
  prominences. 
  

  

  (c) 
  Those 
  of 
  relatively 
  great 
  focal 
  length 
  for 
  recording 
  the 
  

   minute 
  details 
  of 
  the 
  structure 
  of 
  the 
  inner 
  corona. 
  

  

  Revolving 
  diaphragms 
  immediately 
  in 
  front 
  of 
  the 
  plate, 
  like 
  

   the 
  star 
  used 
  by 
  Burckhalter 
  in 
  India, 
  are 
  recommended 
  for 
  

   reducing 
  the 
  brightness 
  of 
  the 
  inner 
  corona 
  to 
  the 
  intensity 
  of 
  

   the 
  mid 
  region, 
  whereby 
  both 
  can 
  be 
  photographed 
  sharply 
  with 
  

   the 
  same 
  exposure. 
  

  

  (5) 
  Photographic 
  search 
  for 
  an 
  intra-Mercurial 
  planet. 
  

  

  (6) 
  Distribution 
  of 
  "coronium" 
  by 
  testing 
  visually 
  and 
  photo- 
  

   graphically 
  the 
  spectrum 
  of 
  different 
  parts 
  of 
  the 
  corona. 
  

  

  (7) 
  Wave 
  length 
  of 
  the 
  green 
  coronal 
  line 
  by 
  photographs 
  

   from 
  a 
  powerful 
  spectrograph. 
  

  

  (8) 
  Photographs 
  of 
  the 
  " 
  flash 
  " 
  spectrum 
  at 
  stations 
  near 
  the 
  

   boundaries 
  of 
  the 
  shadow 
  path, 
  including 
  if 
  possible 
  a 
  study 
  of 
  

   the 
  dark 
  line 
  spectrum 
  before 
  the 
  flash 
  at 
  first 
  contact 
  and 
  after 
  

   the 
  flash 
  at 
  last 
  contact. 
  

  

  (9) 
  The 
  heat 
  radiation 
  of 
  the 
  corona 
  measured 
  by 
  the 
  bolo- 
  

   meter 
  in 
  the 
  streamers 
  and 
  rifts 
  and 
  at 
  various 
  distances 
  from 
  the 
  

   sun's 
  limb. 
  

  

  (10) 
  Photometric 
  observations 
  of 
  the 
  corona 
  at 
  various 
  dis- 
  

   tances 
  from 
  the 
  sun's 
  limb, 
  preferably 
  photographic 
  on 
  account 
  

   of 
  the 
  short 
  duration 
  of 
  totality. 
  

  

  (11) 
  Photometric 
  observations 
  of 
  Mercury. 
  

  

  It 
  is 
  recommended 
  that 
  attempts 
  be 
  made 
  to 
  photograph 
  the 
  

   corona 
  for 
  as 
  many 
  seconds 
  as 
  possible 
  before 
  and 
  after 
  totality, 
  

  

  