﻿166 
  Prof. 
  A. 
  Battelli 
  on 
  the 
  Analogy 
  between 
  

  

  impression 
  a 
  sharp 
  demarcation 
  is 
  generally 
  observed 
  between 
  

   the 
  part 
  acted 
  upon 
  (corresponding 
  to 
  the 
  region 
  above 
  the 
  

   reflector) 
  and 
  the 
  part 
  which 
  remained 
  unaltered 
  (corre- 
  

   sponding 
  to 
  the 
  region 
  beneath). 
  

  

  Observing 
  then 
  the 
  interior 
  of 
  the 
  bulb, 
  one 
  could 
  easily 
  

   perceive, 
  so 
  long 
  as 
  the 
  rarefaction 
  was 
  not 
  very 
  high, 
  the 
  

   luminous 
  pencil 
  of 
  the 
  reflected 
  cathodic 
  rays 
  forming 
  with 
  

   the 
  reflector 
  an 
  angle, 
  which, 
  by 
  the 
  way, 
  could 
  not 
  be 
  

   reckoned 
  as 
  equal 
  to 
  that 
  of 
  the 
  incident 
  pencil 
  ; 
  but 
  mean- 
  

   while 
  the 
  fluorescence, 
  though 
  slight, 
  spread 
  over 
  all 
  the 
  

   inner 
  side 
  of 
  the 
  tube 
  placed 
  above 
  the 
  plane 
  of 
  the 
  reflector. 
  

  

  Whilst 
  by 
  degrees 
  the 
  rarefaction 
  was 
  gradually 
  being 
  

   increased, 
  the 
  reflected 
  pencil 
  of 
  rays 
  became 
  less 
  and 
  less 
  

   distinct 
  ; 
  and 
  near 
  the 
  surface 
  of 
  the 
  reflector 
  there 
  could 
  

   then 
  be 
  noted, 
  especially 
  by 
  means 
  of 
  an 
  opaque 
  surface 
  

   provided 
  with 
  a 
  small 
  opening, 
  a 
  feeble 
  halo 
  (rays 
  expanding 
  

   in 
  all 
  directions), 
  whilst 
  the 
  demarcation-line 
  between 
  the 
  

   inner 
  and 
  outer 
  part 
  of 
  the 
  tube 
  grew 
  more 
  and 
  more 
  distinct. 
  

  

  2nd 
  Experiment. 
  — 
  The 
  cathode 
  of 
  the 
  bulb 
  used 
  in 
  this 
  

   experiment 
  was 
  a 
  plane 
  disk, 
  and 
  the 
  reflector 
  had 
  a 
  spherical 
  

   surface. 
  The 
  luminous 
  cathodic 
  rays 
  striking 
  on 
  the 
  spherical 
  

   reflector 
  were 
  not 
  reflected 
  in 
  a 
  convergent 
  pencil, 
  bat 
  in 
  a 
  

   diminishing 
  and 
  rather 
  divergent 
  one, 
  which, 
  as 
  the 
  rare- 
  

   faction 
  increased, 
  reduced 
  itself 
  into 
  a 
  halo 
  near 
  the 
  surface, 
  

   with 
  an 
  aspect 
  not 
  very 
  dissimilar 
  to 
  the 
  one 
  it 
  assumed 
  when 
  

   the 
  reflector 
  was 
  formed 
  by 
  a 
  plane 
  surface. 
  

  

  Besides 
  this 
  the 
  fluorescence 
  expanded 
  on 
  the 
  inner 
  sides 
  

   of 
  the 
  tube 
  in 
  a 
  manner 
  similar 
  to 
  the 
  case 
  of 
  a 
  plane 
  re- 
  

   flector 
  with 
  a 
  line 
  of 
  demarcation 
  corresponding 
  to 
  the 
  edge 
  

   of 
  the 
  spherical 
  reflector. 
  

  

  These 
  first 
  two 
  experiments 
  prove 
  that 
  it 
  is 
  quite 
  out 
  of 
  

   the 
  question 
  to 
  speak 
  of 
  a 
  completely 
  regular 
  reflexion 
  of 
  the 
  

   cathodic 
  rays. 
  

  

  3rd 
  Experiment. 
  — 
  On 
  the 
  direction 
  taken 
  by 
  the 
  small 
  

   luminous 
  pencil 
  of 
  the 
  cathodic 
  ra^s, 
  reflected 
  by 
  the 
  ordinary 
  

   reflector 
  of 
  the 
  focus-bulb, 
  a 
  second 
  plane 
  reflector 
  was 
  

   placed 
  with 
  an 
  inclination 
  of 
  about 
  45° 
  to 
  the 
  pencil. 
  

  

  This 
  second 
  reflector 
  sent 
  back 
  the 
  rays 
  that 
  fell 
  on 
  it 
  

   in 
  a 
  less 
  condensed 
  pencil 
  than 
  when 
  these 
  same 
  rays 
  reached 
  

   it 
  but 
  vet 
  its 
  action 
  was 
  similar 
  to 
  that 
  of 
  the 
  first 
  reflector, 
  

   with 
  this 
  difference, 
  that 
  the 
  halo 
  round 
  its 
  surface 
  had 
  a 
  

   certain 
  preponderance 
  over 
  the 
  short 
  reflected 
  pencil, 
  which 
  

   appeared 
  faint 
  and 
  fading, 
  and 
  was 
  often 
  invisible. 
  

  

  Uh 
  Experiment. 
  — 
  In 
  the 
  bulb 
  of 
  fig. 
  1 
  instead 
  of 
  the 
  

   photographic 
  cylinder 
  c, 
  a 
  spherical 
  reflector 
  S' 
  was 
  placed 
  

   with 
  its 
  axis 
  in 
  a 
  horizontal 
  position, 
  and 
  the 
  cylinder 
  c' 
  was 
  

  

  