﻿Prof. 
  A. 
  Roiti 
  on 
  the 
  x-Rai/s 
  and 
  the 
  Caihodic 
  Beam. 
  509 
  

  

  with 
  under 
  like 
  conditions 
  have 
  equal 
  power 
  of 
  emission, 
  I 
  

   doubted 
  whether 
  the 
  similarity 
  of 
  my 
  tubes 
  might 
  not 
  have 
  

   been 
  more 
  apparent 
  than 
  real 
  ; 
  for 
  the 
  slightest 
  trace 
  of 
  gas 
  

   contained 
  in 
  the 
  metals 
  or 
  adhering 
  to 
  the 
  walls 
  is 
  sufficient 
  

   to 
  profoundly 
  modify 
  the 
  results 
  of 
  the 
  experiment 
  ; 
  and 
  I 
  

   repeated 
  the 
  experiment, 
  using 
  one 
  tube 
  only. 
  I 
  covered 
  the 
  

   aluminium 
  disk, 
  half 
  internally 
  and 
  half 
  externally, 
  with 
  two 
  

   pieces 
  of 
  the 
  same 
  sheet 
  of 
  magnesium, 
  being 
  careful 
  to 
  fix 
  

   the 
  internal 
  half, 
  which 
  might 
  otherwise, 
  under 
  the 
  influence 
  

   of 
  the 
  disaharge, 
  have 
  been 
  so 
  much 
  agitated 
  as 
  to 
  be 
  entirely 
  

   o\erturned. 
  The 
  disk 
  served 
  as 
  an 
  anode, 
  was 
  in 
  communi- 
  

   cation 
  with 
  the 
  ground, 
  and 
  was 
  protected 
  externally 
  by 
  a 
  

   sheet 
  of 
  lead 
  perforated 
  in 
  the 
  centre. 
  

  

  When 
  I 
  applied 
  a 
  cryptoscope 
  I 
  could 
  observe 
  not 
  the 
  

   slightest 
  difference 
  in 
  brightness 
  on 
  either 
  side 
  of 
  the 
  diameter 
  

   of 
  separation. 
  This 
  proves 
  nothing 
  if 
  one 
  reflects 
  that, 
  wirh 
  

   the 
  concave 
  cathode, 
  the 
  region 
  struck 
  by 
  the 
  cathodic 
  rays 
  

   must 
  be 
  very 
  limited 
  in 
  extent. 
  But 
  I 
  found 
  it 
  also 
  very 
  

   limited 
  when 
  I 
  used 
  a 
  convex 
  cathode, 
  on 
  account 
  of 
  the 
  

   electrostatic 
  action 
  which 
  the 
  cylindrical 
  wall 
  has 
  on 
  the 
  

   pencil, 
  which 
  would 
  otherwise 
  be 
  divergent. 
  

  

  I 
  was 
  able 
  to 
  obtain 
  a 
  fairly 
  uniform 
  illumination 
  of 
  an 
  

   extended 
  area 
  by 
  using 
  the 
  tube 
  represented 
  in 
  fig. 
  2, 
  in 
  

  

  Fig. 
  2. 
  

  

  &:,■:■'■'■//////,} 
  

  

  which 
  I 
  had 
  placed 
  a 
  slightly 
  convex 
  cathode 
  and 
  had 
  fixed 
  

   an 
  aluminium 
  tube 
  to 
  the 
  disk. 
  With 
  this, 
  keeping 
  the 
  

   anodic 
  disk 
  in 
  communication 
  with 
  the 
  filiform 
  aluminium 
  

   electrode 
  and 
  with 
  the 
  ground, 
  I 
  was 
  able 
  to 
  assure 
  myself 
  

   that 
  the 
  half 
  internally 
  uncovered 
  and 
  externally 
  covered 
  bv 
  

   the 
  magnesium 
  gave 
  a 
  greater 
  luminosity 
  to 
  the 
  platino- 
  

  

  