﻿Chemistry 
  and 
  Physics. 
  445 
  

  

  under 
  bombardment 
  ; 
  the 
  total 
  energy 
  available 
  for 
  photography 
  

   falls 
  off 
  as 
  the 
  fourth 
  power 
  of 
  the 
  diameter 
  of 
  the 
  canal-ray 
  

   tube." 
  This 
  quotation 
  from 
  a 
  recent 
  paper 
  by 
  F. 
  W. 
  Aston 
  

   indicates 
  the 
  difficulties 
  which 
  he 
  has 
  largely 
  overcome 
  in 
  design- 
  

   ing 
  the 
  new 
  precision 
  spectrograph 
  briefly 
  described 
  below. 
  

  

  The 
  positive 
  rays 
  after 
  arriving 
  at 
  the 
  cathode 
  face 
  pass 
  

   through 
  two 
  very 
  fine 
  parallel 
  slits 
  of 
  special 
  construction, 
  and 
  

   the 
  emergent 
  thin 
  ribbon 
  of 
  rays 
  is 
  spread 
  out 
  into 
  a 
  spectrum 
  

   by 
  the 
  electric 
  field 
  established 
  between 
  two 
  parallel 
  plates. 
  The 
  

   planes 
  of 
  these 
  plates 
  are 
  appropriately 
  tilted 
  with 
  respect 
  to 
  

   the 
  plane 
  determined 
  by 
  the 
  long 
  axes 
  of 
  the 
  two 
  slits 
  in 
  order 
  to 
  

   give 
  free 
  passage 
  to 
  the 
  rays 
  in 
  their 
  curved 
  paths. 
  The 
  slit 
  

   boundaries 
  were 
  made 
  of 
  aluminium 
  as 
  it 
  was 
  found 
  that 
  this 
  

   metal 
  suffers 
  no 
  appreciable 
  disintegration 
  by 
  bombardment. 
  

   The 
  loss 
  by 
  collision 
  (mentioned 
  above) 
  was 
  minimized 
  by 
  

   exhausting 
  the 
  region 
  between 
  the 
  slits 
  to 
  as 
  high 
  a 
  degree 
  as 
  

   possible. 
  After 
  leaving 
  the 
  electric 
  field 
  the 
  widened 
  beam 
  of 
  

   rays 
  fell 
  approximately 
  normally 
  upon 
  a 
  stop 
  or 
  diaphragm 
  

   which 
  was 
  so 
  placed 
  and 
  adjusted 
  as 
  to 
  transmit 
  only 
  a 
  selected 
  

   portion 
  of 
  the 
  beam. 
  After 
  this, 
  the 
  rays 
  transmitted 
  traversed 
  

   a 
  magnetic 
  field 
  between 
  the 
  circular 
  pole-pieces 
  of 
  an 
  electro- 
  

   magnet. 
  The 
  direction 
  and 
  sense 
  of 
  the 
  magnetic 
  field 
  were 
  

   such 
  as 
  to 
  bend 
  the 
  paths 
  of 
  the 
  rays 
  in 
  a 
  direction 
  exactly 
  oppo- 
  

   site 
  to 
  that 
  of 
  the 
  deflection 
  produced 
  by 
  the 
  electric 
  field. 
  

  

  This 
  arrangement 
  of 
  parts 
  has 
  the 
  effect 
  of 
  bringing 
  the 
  rays 
  

   to 
  sharp 
  linear 
  foci 
  in 
  a 
  plane 
  which 
  intersects 
  the 
  plane 
  deter- 
  

   mined 
  by 
  the 
  two 
  slits 
  at 
  about 
  the 
  center 
  of 
  the 
  electric 
  field 
  and 
  

   which 
  makes 
  a 
  certain 
  angle 
  with 
  the 
  undeviated 
  ribbon. 
  In 
  

   short, 
  the 
  rays 
  act 
  as 
  if 
  they 
  had 
  come 
  from 
  an 
  effective 
  line 
  

   source 
  in 
  the 
  middle 
  of 
  the 
  "electric 
  field 
  so 
  that 
  the 
  focusing 
  is 
  

   efficient 
  both 
  as 
  regards 
  definition 
  and 
  intensity. 
  Obviously, 
  the 
  

   photographic 
  plate 
  is 
  placed 
  in 
  the 
  focal 
  plane 
  mentioned 
  above. 
  

   The 
  author 
  says 
  : 
  ' 
  ' 
  The 
  field 
  between 
  the 
  plates 
  can 
  be 
  adjusted 
  

   to 
  allow 
  the 
  brightest 
  part 
  of 
  the 
  electric 
  spectrum 
  to 
  be 
  used 
  

   which, 
  as 
  has 
  been 
  shown, 
  is 
  in 
  general 
  the 
  same 
  for 
  all 
  normal 
  

   rays 
  under 
  steady 
  discharge, 
  and 
  the 
  values 
  of 
  e/m 
  can 
  be 
  com- 
  

   pared 
  very 
  accurately 
  from 
  the 
  positions 
  of 
  their 
  lines 
  relative 
  

   to 
  those 
  of 
  standard 
  elements 
  which 
  can 
  be 
  brought 
  to 
  any 
  desired 
  

   position 
  on 
  the 
  plate 
  by 
  varying 
  the 
  magnetic 
  field 
  strength. 
  ' 
  ' 
  — 
  

   Phil 
  Mag., 
  38, 
  707, 
  1919. 
  h. 
  s. 
  u. 
  

  

  6. 
  The 
  Constitution 
  of 
  Atmospheric 
  Neon. 
  — 
  The 
  primary 
  

   object 
  which 
  F. 
  W. 
  Aston 
  had 
  in 
  mind 
  while 
  designing 
  the 
  posi- 
  

   tive 
  ray 
  spectrograph, 
  very 
  briefly 
  described 
  in 
  the 
  preceding 
  

   notice, 
  was 
  to 
  develop 
  a 
  method 
  for 
  producing 
  "mass-spectra" 
  

   which 
  would 
  give 
  a 
  sufficiently 
  high 
  degree 
  of 
  precision 
  to 
  enable 
  

   a 
  final 
  decision 
  to 
  be 
  made 
  concerning 
  the 
  alleged 
  complex 
  nature 
  

   of 
  neon. 
  In 
  a 
  later 
  paper 
  the 
  same 
  investigator 
  gives 
  a 
  detailed 
  

   account 
  of 
  the 
  important 
  results 
  obtained 
  with 
  his 
  new 
  appara- 
  

   tus. 
  It 
  is 
  not 
  necessary 
  to 
  enter 
  into 
  the 
  details 
  of 
  the 
  research 
  

  

  