﻿712 
  - 
  Mr. 
  H. 
  B. 
  Keene 
  on 
  the 
  

  

  the 
  observed 
  fact 
  that 
  the 
  a 
  particle 
  in 
  its 
  flight 
  carries 
  two 
  

   unit 
  positive 
  charges. 
  

  

  The 
  observations 
  on 
  the 
  scattering 
  o£ 
  a 
  particles 
  by 
  matter 
  

   in 
  general 
  afford 
  strong 
  experimental 
  evidence 
  for 
  the 
  theory 
  

   that 
  the 
  atom 
  consists 
  of 
  a 
  positively 
  charged 
  nucleus 
  of 
  

   minute 
  dimensions 
  surrounded 
  by 
  a 
  compensating 
  distribu- 
  

   tion 
  of 
  negative 
  electrons. 
  The 
  charge 
  on 
  the 
  nucleus 
  for 
  

   heavy 
  atoms 
  is 
  approximately 
  ^Ae, 
  where 
  A 
  is 
  the 
  atomic 
  

   weight 
  and 
  e 
  the 
  electronic 
  charge. 
  The 
  experiments 
  in 
  this 
  

   paper 
  on 
  the 
  scattering 
  of 
  simple 
  gases 
  indicate 
  that 
  the 
  

   hydrogen 
  atom 
  has 
  the 
  simplest 
  possible 
  structure 
  of 
  a 
  

   nucleus 
  with 
  one 
  unit 
  charge, 
  and 
  helium 
  comes 
  next 
  with 
  

   a 
  nucleus 
  of 
  two 
  unit 
  charges. 
  This 
  simple 
  structure 
  for 
  

   hydrogen 
  and 
  helium 
  atoms 
  has 
  been 
  assumed 
  by 
  Bohr* 
  in 
  

   a 
  recent 
  interesting 
  paper 
  on 
  the 
  constitution 
  of 
  atoms, 
  and 
  

   has 
  been 
  shown 
  by 
  him 
  to 
  yield 
  very 
  promising 
  results. 
  

  

  We 
  desire 
  to 
  express 
  our 
  thanks 
  to 
  Dr. 
  Pring 
  for 
  his 
  

   assistance 
  in 
  preparing 
  and 
  purifying 
  the 
  gases 
  employed. 
  

  

  University 
  of 
  Manchester, 
  

   July 
  1918. 
  

  

  LVIII. 
  On 
  the 
  Transmission 
  of 
  X 
  Rays 
  through 
  Metals. 
  By 
  

   H. 
  B. 
  Keene, 
  Assistant 
  Lecturer 
  in 
  Physics 
  at 
  the 
  Uni- 
  

   versity 
  of 
  Birmingham^. 
  

  

  MANY 
  investigators 
  have 
  studied 
  the 
  transmission 
  of 
  

   X 
  rays 
  through 
  metal 
  sheets 
  and 
  the 
  distribution 
  

   of 
  the 
  " 
  incident 
  " 
  and 
  " 
  emergent 
  " 
  radiation. 
  The 
  method 
  

   of 
  measurement 
  adopted 
  has 
  been 
  an 
  electrical 
  one, 
  the 
  

   photographic 
  method 
  having 
  fallen 
  into 
  disuse. 
  Its 
  revival 
  

   in 
  the 
  experiments 
  of 
  Messrs. 
  Friedrich, 
  Knipping, 
  and 
  Laue 
  

   on 
  the 
  transmission 
  of 
  X 
  rays 
  through 
  crystals 
  and 
  the 
  re- 
  

   markable 
  results 
  obtained, 
  suggested 
  that 
  interesting 
  results 
  

   might 
  follow 
  with 
  materials 
  other 
  than 
  crystals 
  if 
  the 
  ioniza- 
  

   tion 
  chamber 
  was 
  replaced 
  by 
  the 
  photographic 
  plate. 
  It 
  

   seemed 
  probable 
  that 
  the 
  ionization 
  method 
  might 
  have 
  

   overlooked 
  certain 
  effects 
  which 
  the 
  photographic 
  plate 
  

   would 
  record. 
  A 
  photographic 
  investigation 
  of 
  the 
  " 
  inci- 
  

   dent 
  " 
  and 
  " 
  emergent 
  " 
  radiation 
  from 
  metal 
  sheets 
  led 
  to 
  

   some 
  striking 
  results 
  which 
  are 
  described 
  in 
  the 
  present 
  

   paper. 
  

  

  * 
  Phil. 
  Mag. 
  July 
  1913. 
  

  

  t 
  Communicated 
  by 
  Prof. 
  J. 
  H. 
  Poynting, 
  F.R.S. 
  

  

  