﻿388 
  C. 
  B. 
  Thwing 
  — 
  Color 
  Photography. 
  

  

  5. 
  Regarding 
  the 
  instrument 
  as 
  in 
  the 
  figure, 
  rotate 
  it 
  around 
  

  

  the 
  line 
  of 
  sight 
  and 
  in 
  the 
  plane 
  of 
  the 
  paper, 
  thus 
  causing 
  

   any 
  air 
  or 
  vapor 
  accumulated 
  in 
  the 
  vacant 
  space 
  to 
  pass 
  

   into 
  the 
  cistern, 
  whence 
  it 
  can 
  no 
  more 
  pass 
  into 
  other 
  parts 
  

   of 
  the 
  cavity. 
  

  

  6. 
  Repeat 
  the 
  foregoing 
  manipulations 
  in 
  order, 
  until 
  the 
  vacuum 
  

  

  in 
  V 
  is 
  as 
  nearly 
  perfect 
  as 
  possible. 
  (Probably 
  No. 
  1 
  need 
  

   not 
  be 
  repeated 
  often.) 
  

  

  Doubtless 
  the 
  apparatus 
  would 
  work 
  well 
  if 
  made 
  without 
  

   the 
  return 
  tube 
  T' 
  and 
  its 
  prolongation 
  yy, 
  being 
  sealed 
  at 
  D 
  

   and 
  E 
  ; 
  but 
  the 
  complete 
  loop 
  has 
  evident 
  advantages, 
  among 
  

   which 
  is 
  the 
  fact 
  that 
  it 
  allows 
  the 
  tubes 
  to 
  be 
  of 
  small 
  bore 
  

   without 
  impeding 
  the 
  flow 
  of 
  the 
  mercury 
  and 
  the 
  transfer 
  of 
  

   air- 
  bubbles, 
  thus 
  greatly 
  diminishing 
  the 
  amount 
  of 
  mercury 
  

   required. 
  

  

  The 
  principal 
  features 
  of 
  this 
  construction 
  occurred 
  to 
  me 
  

   some 
  two 
  years 
  since, 
  but 
  my 
  attention 
  was 
  taken 
  from 
  it 
  by 
  

   other 
  matters 
  until 
  recalled 
  by 
  reading 
  an 
  account 
  of 
  the 
  

   method 
  proposed 
  by 
  G. 
  Gruglieimo,* 
  this 
  method 
  being 
  essen- 
  

   tially 
  the 
  same 
  as 
  that 
  involved 
  in 
  the 
  foregoing 
  manipula- 
  

   tions 
  ; 
  but 
  his 
  apparatus 
  seems 
  to 
  me 
  less 
  perfect 
  and 
  conven- 
  

   ient 
  than 
  that 
  described 
  above. 
  He 
  claims 
  that 
  this 
  method 
  

   gives 
  better 
  results 
  than 
  that 
  of 
  boiling 
  the 
  mercury, 
  but 
  it 
  is 
  

   evident 
  that 
  heat 
  can 
  easily 
  be 
  used 
  with 
  the 
  loop 
  form 
  of 
  

   tube, 
  if 
  desired. 
  

  

  Boulder, 
  Colorado, 
  July 
  29, 
  1891. 
  

  

  Aet. 
  XXXVIII. 
  — 
  Color 
  Photography 
  by 
  Lippmann? 
  8 
  

   Process 
  ; 
  by 
  Charles 
  B. 
  Thwing, 
  Evanston, 
  111. 
  

  

  In 
  a 
  communication 
  to 
  the 
  Academie 
  des 
  Sciences 
  on 
  the 
  

   second 
  of 
  February 
  last, 
  M. 
  G-. 
  Lippmann 
  opened 
  an 
  entirely 
  

   new 
  line 
  of 
  experimentation 
  on 
  the 
  problem 
  of 
  the 
  photo- 
  

   graphic 
  reproduction 
  of 
  the 
  colors 
  of 
  nature. 
  To 
  Lippmann's 
  

   account 
  of 
  his 
  discovery 
  is 
  appended 
  in 
  Comptes 
  Rendus 
  a 
  

   note 
  by 
  Mons. 
  Edw. 
  Becquerel 
  to 
  the 
  effect 
  that 
  the 
  process 
  

   of 
  Lippmann 
  differs 
  radically 
  from 
  the 
  discovery 
  made 
  by 
  him- 
  

   self 
  in 
  1848, 
  in 
  that 
  while 
  Becquerel 
  was 
  able 
  by 
  photo-chem- 
  

   ical 
  means 
  to 
  produce 
  a 
  colored 
  image 
  of 
  the 
  spectrum 
  which 
  

   could 
  not 
  be 
  exposed 
  to 
  light 
  since 
  the 
  action 
  of 
  the 
  usual 
  fix- 
  

   ing 
  agents 
  reduced 
  the 
  deposit 
  to 
  a 
  mere 
  film 
  of 
  metallic 
  silver, 
  

   Lippmann, 
  on 
  the 
  other 
  hand, 
  had 
  by 
  a 
  physical 
  process 
  ob- 
  

   tained 
  an 
  image 
  which 
  retains 
  its 
  colors 
  after 
  treatment 
  with 
  

   hyposulphite 
  of 
  soda, 
  and 
  is, 
  therefore, 
  as 
  permanent 
  as 
  an 
  

  

  * 
  Atti 
  della 
  reale 
  Accad. 
  dei 
  Lincei, 
  August, 
  1890. 
  

  

  