﻿510 
  Prof. 
  A. 
  Roiti 
  on 
  the 
  x-Mays 
  and 
  the 
  Cathodic 
  Beam. 
  

  

  cyanide 
  of 
  barium 
  of 
  the 
  cryptoscope 
  than 
  did 
  the 
  other 
  half. 
  

   Hence 
  it 
  may 
  be 
  maintained 
  that 
  aluminium 
  has 
  a 
  higher 
  

   power 
  of 
  emission 
  than 
  magnesium. 
  

  

  It 
  then 
  occurred 
  to 
  me 
  to 
  compare 
  other 
  metals 
  in 
  the 
  

   same 
  way, 
  by 
  twos 
  ; 
  covering 
  the 
  aluminium 
  disk 
  internally 
  

   half 
  with 
  the 
  metal 
  A 
  and 
  half 
  with 
  the 
  metal 
  B, 
  and 
  placing 
  

   B 
  externally 
  with 
  regard 
  to 
  A, 
  and 
  A 
  with 
  regard 
  to 
  B. 
  

  

  In 
  the 
  following 
  table 
  I 
  have 
  arranged 
  the 
  various 
  metals 
  

   on 
  an 
  increasing 
  scale 
  of 
  emissive 
  power. 
  The 
  first 
  column 
  

   shows 
  the 
  thickness 
  of 
  the 
  plates 
  used 
  ; 
  the 
  third 
  and 
  fourth 
  

   their 
  density 
  and 
  atomic 
  weights. 
  

  

  mm. 
  0-24 
  Magnesium 
  1*74 
  24*38 
  

  

  1-72 
  Aluminium 
  2*67 
  27*1 
  

  

  0-17 
  Iron 
  7'79 
  06 
  

  

  0*10 
  Copper 
  8-95 
  63 
  

  

  0*10 
  Zinc 
  6-92 
  654: 
  

  

  0-15 
  *Tin 
  7-29 
  118-1 
  

  

  0-10 
  Silver 
  10-47 
  107-94 
  

  

  0-13 
  Cadmium 
  8-67 
  112 
  

  

  0-012 
  Platinum 
  21-3 
  194-3 
  

  

  0-06 
  Lead 
  11-37 
  206-9 
  

  

  It 
  is 
  evident 
  that 
  the 
  power 
  of 
  emission 
  for 
  ay-rays 
  is 
  

   determined 
  neither 
  by 
  density 
  nor 
  by 
  atomic 
  volume, 
  but 
  that 
  

   (with 
  the 
  exception 
  of 
  tin, 
  perhaps 
  because 
  I 
  used 
  commercial 
  

   and 
  therefore 
  impure 
  metal) 
  it 
  increases 
  regularly 
  with 
  the 
  

   atomic 
  weight. 
  

  

  Should 
  this 
  law 
  prove 
  general 
  it 
  would 
  have 
  a 
  theoretic 
  

   bearing 
  of 
  no 
  small 
  importance. 
  Meanwhile 
  I 
  restrict 
  myself 
  

   to 
  observing 
  that 
  there 
  should 
  be 
  an 
  advantage, 
  unless 
  its 
  

   easy 
  fusibility 
  proves 
  a 
  hindrance, 
  in 
  the 
  use 
  of 
  lead 
  instead 
  

   of 
  platinum 
  as 
  an 
  anticathode 
  in 
  the 
  Rontgen 
  tubes. 
  Lead 
  

   placed 
  in 
  sheets 
  on 
  aluminium 
  should 
  serve 
  still 
  better, 
  as 
  I 
  

   intend 
  proving. 
  

  

  (Addition 
  during 
  the 
  correction 
  of 
  the 
  proofs). 
  While 
  com- 
  

   mercial 
  tin(*) 
  had 
  to 
  be 
  placed 
  between 
  zinc 
  and 
  silver, 
  that 
  

   furnished 
  as 
  pure 
  by 
  Merck, 
  of 
  Darmstadt, 
  and 
  reduced 
  to 
  a 
  

   sheet 
  of 
  0*11 
  mm. 
  in 
  thickness, 
  shows 
  a 
  considerably 
  greater 
  

   power 
  of 
  emission 
  ; 
  greater 
  than 
  that 
  of 
  cadmium. 
  We 
  may 
  

   therefore 
  assert 
  that 
  the 
  metals 
  of 
  greater 
  atomic 
  weight 
  emit 
  

   x-rays 
  of 
  greater 
  intensity. 
  

   Florence, 
  August 
  20, 
  1897. 
  

  

  