﻿Prof. 
  A. 
  Roiti 
  on 
  the 
  x-Bays 
  and 
  the 
  Cathodic 
  Beam. 
  503 
  

  

  It 
  is 
  far 
  different 
  if 
  the 
  Abbe 
  theory 
  be 
  relegated 
  to 
  its 
  proper 
  

   place 
  and 
  proportion. 
  Then 
  such 
  " 
  lucky" 
  objectives 
  as 
  the 
  

   above 
  assume 
  a 
  very 
  marked 
  significance, 
  and 
  hold 
  out 
  a 
  world 
  

   of 
  promise 
  : 
  in 
  them 
  and 
  in 
  what 
  they 
  tell 
  us 
  lies 
  the 
  future 
  of 
  

   microscopy. 
  Not 
  the 
  best 
  even 
  of 
  them 
  is 
  probably 
  perfectly 
  

   corrected 
  for 
  all 
  its 
  zones 
  ; 
  but 
  the 
  best 
  of 
  them 
  reveal 
  a 
  

   marvellous 
  standard 
  of 
  approach 
  to 
  this 
  ; 
  and 
  with 
  that 
  we 
  find 
  

   ever 
  associated 
  an 
  increase 
  of 
  that 
  practicable 
  cone 
  of 
  hetero- 
  

   geneous 
  light 
  which 
  we 
  have 
  found 
  so 
  all-important 
  to 
  true 
  

   contours. 
  And 
  with 
  this 
  we 
  get 
  further 
  revelation. 
  More 
  

   minuteness 
  we 
  do 
  not 
  indeed 
  get 
  ; 
  for 
  that 
  we 
  can 
  look 
  only 
  to 
  

   the 
  1*63 
  lens. 
  But 
  we 
  have 
  a 
  world 
  of 
  structure 
  to 
  learn 
  yet, 
  

   within 
  the 
  resolution 
  of 
  our 
  present 
  lenses 
  ; 
  and 
  for 
  that 
  we 
  

   are 
  only 
  waiting 
  better 
  condensers 
  and 
  better 
  correction. 
  It 
  

   was 
  only 
  recently 
  that 
  the 
  protoplasm 
  so 
  long 
  written 
  of 
  as 
  

   " 
  structureless 
  jelly," 
  yielded 
  up 
  some 
  at 
  least 
  of 
  its 
  marvellous 
  

   and 
  minute 
  structure, 
  which 
  can 
  only 
  be 
  seen 
  by 
  English, 
  

   wide-cone 
  methods, 
  with 
  one 
  of 
  the 
  exceptionally-perfect 
  

   objectives 
  here 
  referred 
  to 
  ; 
  whose 
  significance, 
  however, 
  as 
  

   we 
  have 
  seen, 
  is 
  not 
  yet 
  recognized 
  on 
  the 
  Continent 
  as 
  

   it 
  is 
  in 
  England, 
  and 
  even 
  here 
  only 
  by 
  the 
  few. 
  It 
  may 
  

   be 
  beyond 
  us 
  to-day 
  to 
  discover 
  the 
  minute 
  departures 
  from 
  

   type 
  which 
  cause 
  the 
  superiority 
  of 
  the 
  few 
  phenomenal 
  lenses 
  : 
  

   it 
  is 
  no 
  easy 
  thing 
  to 
  ascertain 
  precisely 
  what 
  it 
  is, 
  in 
  a 
  

   lens 
  one 
  of 
  whose 
  components 
  may 
  not 
  exceed 
  a 
  hemisphere 
  

   Y^g 
  of 
  an 
  inch 
  in 
  diameter. 
  But 
  the 
  superiority 
  is 
  there 
  ; 
  it 
  

   has 
  been 
  attained 
  ; 
  and 
  we 
  may 
  cherish 
  reasonable 
  hopes 
  of 
  

   such 
  discovery. 
  We 
  may 
  anticipate 
  that 
  the 
  present 
  rarest 
  

   excellence 
  may 
  be 
  reached 
  yet 
  as 
  a 
  standard, 
  more 
  generally 
  

   procurable 
  by 
  the 
  scientific 
  investigator 
  ; 
  that 
  the 
  very 
  best 
  

   of 
  all 
  may 
  even 
  be 
  further 
  improved 
  in 
  correction 
  in 
  some 
  

   degree. 
  If 
  it 
  be 
  so, 
  such 
  advances 
  w 
  7 
  ill 
  not 
  be 
  barren 
  of 
  

   results 
  in 
  research. 
  The 
  microscopist 
  may 
  yet 
  hope 
  and 
  take 
  

  

  courage. 
  

  

  LII. 
  Whether 
  the 
  x-rays 
  already 
  exist 
  in 
  the 
  Cathodic 
  Seam 
  

   which 
  'produces 
  them. 
  By 
  Prof. 
  A. 
  Roiti*. 
  

  

  I. 
  

  

  ri^HE 
  question 
  placed 
  at 
  the 
  head 
  of 
  this 
  communication 
  

   JL 
  will 
  be 
  answered 
  by 
  most 
  people 
  in 
  the 
  negative 
  ; 
  but 
  

   there 
  are 
  exceptions, 
  and 
  it 
  may 
  therefore 
  be 
  well 
  to 
  do 
  away 
  

   with 
  all 
  doubts 
  on 
  the 
  subject. 
  

  

  * 
  From 
  the 
  Bendiconti 
  delta 
  R. 
  Accademia 
  del 
  Lincei 
  (Classe 
  di 
  sc. 
  

   fis., 
  mat. 
  e 
  uat.). 
  vol. 
  vi. 
  pp. 
  128-129. 
  Communicated 
  by 
  the 
  Author. 
  

  

  2 
  M 
  2 
  

  

  