﻿504 
  Prof. 
  A. 
  Roiti 
  on 
  the 
  x-Rays 
  and 
  the 
  Cathodic 
  Beam. 
  

  

  The 
  jf-rays 
  differ 
  from 
  the 
  cathode-rays 
  in 
  that 
  they 
  cannot 
  

   be 
  deflected 
  by 
  a 
  magnet, 
  and 
  in 
  that 
  they 
  possess 
  a 
  greater 
  

   penetrating 
  power. 
  Yet 
  this 
  is 
  no 
  hard 
  and 
  fast 
  distinction 
  ; 
  

   for 
  as 
  there 
  are 
  cathodic 
  rays 
  which 
  can 
  be 
  more 
  or 
  less 
  

   deflected, 
  so 
  there 
  are 
  .r-rays 
  capable 
  of 
  penetrating 
  to 
  a 
  

   greater 
  or 
  smaller 
  degree 
  into 
  various 
  substances. 
  And 
  on 
  

   the 
  border 
  between 
  the 
  two, 
  although 
  we 
  cannot 
  yet 
  assert, 
  

   we 
  cannot 
  with 
  certainty 
  deny 
  the 
  existence 
  of 
  cathode-rays 
  

   that 
  cannot 
  be 
  deflected, 
  and 
  of 
  A'-rays 
  that 
  canto 
  some 
  extent 
  

   be 
  turned 
  aside 
  by 
  intense 
  magnetic 
  action 
  ; 
  while, 
  on 
  the 
  

   other 
  hand, 
  if 
  the 
  various 
  material 
  mediums 
  are 
  turbid 
  for 
  

   the 
  cathode-rays, 
  they 
  are 
  not 
  perfectly 
  transparent 
  to 
  the 
  

   A'-rays. 
  

  

  Since 
  matters 
  stand 
  thus, 
  one 
  may 
  be 
  allowed 
  to 
  main- 
  

   tain 
  in 
  opposition 
  to 
  the 
  English, 
  who 
  continue 
  to 
  adduce 
  

   excellent 
  reasons 
  in 
  defence 
  of 
  Crookes's 
  theory 
  of 
  radiating 
  

   matter, 
  that 
  the 
  two 
  kinds 
  of 
  rays 
  are 
  not 
  essentially 
  different, 
  

   bat 
  that 
  they 
  gradually 
  merge 
  into 
  each 
  other. 
  Rontgen 
  

   himself, 
  in 
  his 
  third 
  communication*, 
  seems 
  inclined 
  to 
  admit 
  

   this. 
  

  

  But 
  this 
  is 
  a 
  very 
  different 
  thing 
  from 
  asserting 
  that 
  the 
  

   A-rays 
  are 
  derived 
  from 
  the 
  cathode-rays 
  by 
  a 
  simple 
  process 
  

   of 
  subtraction. 
  

  

  Among 
  the 
  various 
  attempts 
  at 
  proving 
  this 
  last 
  assertion 
  

   I 
  must 
  name 
  those 
  of 
  my 
  countrymen 
  f 
  . 
  I 
  refrain, 
  however, 
  

   from 
  analysing 
  them 
  minutely, 
  as 
  I 
  am 
  anxious 
  to 
  avoid 
  here 
  

   any 
  appearance 
  of 
  polemic. 
  Besides, 
  a 
  very 
  little 
  thought 
  

   will 
  be 
  sufficient 
  to 
  confute 
  them 
  if 
  the 
  following 
  conside- 
  

   rations 
  be 
  borne 
  in 
  mind. 
  

  

  1. 
  If 
  we 
  attempt 
  to 
  determine 
  dispersion 
  by 
  observing 
  the 
  

   variations 
  of 
  potential 
  presented 
  by 
  a 
  conductor 
  placed 
  in 
  a 
  

   discharging-tube 
  (whether 
  subjected 
  or 
  not 
  to 
  magnetic 
  action), 
  

   we 
  find 
  it 
  impossible 
  to 
  decide 
  whence 
  the 
  dispersive 
  action 
  

   comes 
  and 
  what 
  way 
  it 
  follows 
  ; 
  because 
  the 
  distribution 
  and 
  

   the 
  fluctuations 
  of 
  the 
  electricity 
  within 
  the 
  tube 
  cannot 
  yet 
  

   be 
  rightly 
  determined 
  J 
  ; 
  and 
  because 
  the 
  phenomenon 
  is 
  

  

  * 
  Sitzungsberichte 
  der 
  Akadeniie 
  zu 
  Berlin, 
  vom 
  13 
  Mai, 
  1897, 
  vol. 
  xxvi. 
  

   p. 
  576. 
  

  

  f 
  A. 
  Battelli, 
  N. 
  Cimento, 
  ser. 
  4, 
  vol. 
  iii. 
  p. 
  193, 
  and 
  vol. 
  v. 
  p. 
  386 
  ; 
  

   Phil. 
  Mag. 
  Feb. 
  1898. 
  A. 
  Battelli 
  and 
  A. 
  Garbasso, 
  N. 
  Cimento, 
  vol. 
  iii. 
  

   p. 
  289, 
  vol. 
  iv. 
  p. 
  129, 
  vol. 
  vi. 
  p. 
  5. 
  

  

  % 
  And, 
  in 
  fact, 
  by 
  a 
  slight 
  change 
  in 
  the 
  conditions 
  of 
  the 
  experiments 
  

   contradictory 
  results 
  are 
  produced. 
  For 
  example, 
  Battelli 
  and 
  Gar 
  basso 
  

   (N. 
  Cimento, 
  vol. 
  iv. 
  p. 
  129, 
  and 
  vol. 
  vi. 
  p. 
  5) 
  find 
  that 
  the 
  cathodic 
  rays 
  

   induce 
  a 
  positive 
  discharge 
  un 
  an 
  insulated 
  conductor 
  (in 
  the 
  last 
  notice 
  

   neyative 
  is 
  a 
  printer's 
  error); 
  while 
  before 
  them 
  Perrin 
  (Compt. 
  Rend. 
  

   vol. 
  cxxi. 
  p. 
  792) 
  had 
  found 
  it 
  negative. 
  

  

  