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  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  Cambridge, 
  where 
  are 
  greater 
  facilities 
  for 
  work 
  of 
  this 
  nature. 
  The 
  

   first 
  experiments 
  at 
  the 
  Fogg 
  Museum, 
  occupying 
  a 
  three 
  months' 
  

   leave 
  of 
  absence 
  from 
  the 
  Minneapolis 
  Institute, 
  proved 
  that 
  the 
  

   X 
  ray 
  does 
  no 
  injury 
  to 
  works 
  of 
  art. 
  And 
  the 
  last 
  18 
  months 
  have 
  

   been 
  devoted, 
  directly 
  under 
  the 
  auspices 
  of 
  the 
  Fogg 
  Museum, 
  to 
  

   the 
  forming 
  of 
  a 
  collection 
  of 
  X-ray 
  films 
  varied 
  in 
  its 
  scope. 
  This 
  

   has 
  been 
  possible 
  through 
  the 
  further 
  cooperation 
  of 
  the 
  Cleveland 
  

   Museum 
  and 
  the 
  interest 
  of 
  museum 
  officials 
  in 
  New 
  York, 
  Paris, 
  

   Berlin, 
  Chicago, 
  Boston, 
  Philadelphia, 
  London, 
  Brussels, 
  Antwerp, 
  

   Bruges, 
  and 
  Ghent. 
  

  

  As 
  a 
  result 
  of 
  cooperative 
  effort 
  and 
  a 
  year 
  and 
  a 
  half 
  of 
  research, 
  

   much 
  information 
  has 
  been 
  gained 
  about 
  artists 
  and 
  paintings, 
  but 
  

   little 
  about 
  X-ray 
  principles. 
  The 
  principle 
  utilized 
  is 
  similar 
  to 
  

   that 
  used 
  for 
  diagnostical 
  work 
  in 
  hospitals. 
  Anyone 
  who 
  has 
  been 
  

   X 
  rayed 
  for 
  a 
  broken 
  bone 
  knows 
  something 
  about 
  it. 
  The 
  bulb, 
  

   placed 
  on 
  one 
  side 
  of 
  the 
  object 
  to 
  be 
  examined, 
  sends 
  out 
  penetrating 
  

   " 
  waves 
  " 
  which 
  cast 
  shadows 
  of 
  objects 
  in 
  their 
  path 
  upon 
  a 
  sensitive 
  

   film, 
  placed 
  on 
  the 
  other 
  side 
  of 
  the 
  object. 
  In 
  the 
  body, 
  bone 
  is 
  

   denser 
  than 
  flesh 
  and 
  throws 
  a 
  darker 
  shadow. 
  In 
  a 
  picture, 
  some 
  

   pigments 
  are 
  denser 
  than 
  others 
  or 
  more 
  thickly 
  applied. 
  Of 
  course, 
  

   the 
  total 
  density 
  of 
  the 
  body 
  is 
  greater 
  than 
  that 
  of 
  a 
  painting, 
  

   whether 
  on 
  wood 
  or 
  canvass. 
  This 
  means 
  that 
  the 
  exposure 
  used 
  in 
  

   X 
  raying 
  pictures 
  must 
  be 
  considerably 
  less. 
  Furthermore, 
  the 
  

   lower 
  the 
  voltage, 
  the 
  more 
  delicate, 
  or 
  selective, 
  the 
  ray, 
  supposedly, 
  

   which 
  is 
  an 
  advantage 
  in 
  bringing 
  out 
  the 
  difference 
  between 
  pig- 
  

   ments 
  only 
  slightly 
  varied 
  in 
  density. 
  

  

  During 
  a 
  year 
  and 
  a 
  half 
  it 
  might 
  have 
  been 
  possible 
  to 
  develop 
  

   a 
  highly 
  specialized 
  " 
  technique 
  " 
  which 
  v/ould 
  fall 
  approximately 
  

   halfway 
  between 
  that 
  used 
  for 
  ordinary 
  medical 
  work 
  and 
  that 
  used 
  

   in 
  the 
  most 
  delicate 
  treatment 
  of 
  skin 
  diseases. 
  But 
  the 
  results 
  so 
  far 
  

   obtained 
  have 
  justified 
  a 
  continuation 
  of 
  the 
  " 
  technique 
  " 
  first 
  de- 
  

   veloped 
  and 
  now 
  in 
  use. 
  The 
  fact 
  is 
  that 
  a 
  difference 
  of 
  5,000 
  volts 
  

   one 
  way 
  or 
  another 
  in 
  the 
  exposure 
  of 
  the 
  same 
  picture 
  was 
  found 
  to 
  

   yield 
  no 
  appreciable 
  differences 
  in 
  the 
  films, 
  and 
  that 
  a 
  difference 
  of 
  

   10,000 
  volts 
  more 
  or 
  less 
  than 
  the 
  middle 
  or 
  best 
  exposure 
  is 
  negli- 
  

   gible. 
  For 
  each 
  picture 
  there 
  is 
  one 
  exposure 
  which 
  gives 
  the 
  utmost 
  

   definition. 
  But 
  practical 
  exposures 
  can 
  usually 
  be 
  made 
  with 
  an 
  

   intensity 
  of 
  between 
  15,000 
  and 
  50,000 
  volts. 
  

  

  The 
  reason 
  for 
  this 
  wide 
  range 
  may 
  be 
  found 
  through 
  study 
  of 
  

   the 
  tables 
  of 
  density 
  of 
  the 
  materials 
  which 
  go 
  into 
  the 
  making 
  of 
  

   a 
  picture. 
  These 
  are 
  presented 
  in 
  the 
  authoritative 
  works 
  by 
  Prof. 
  

   A. 
  P. 
  Laurie 
  and 
  Sir 
  Arthur 
  H. 
  Church, 
  dealing, 
  respectively, 
  with 
  

   the 
  pigments 
  of 
  the 
  old 
  masters 
  and 
  the 
  chemistry 
  of 
  paints. 
  Simple 
  

   experiments 
  assert 
  the 
  same 
  conclusion. 
  When 
  a 
  chart 
  of 
  many 
  

  

  