﻿on 
  Columnar 
  Ionization. 
  

  

  515 
  

  

  The 
  electrometer 
  was 
  of 
  the 
  Dolezalek 
  pattern 
  with 
  a 
  

   platinum 
  suspension, 
  and 
  had 
  a 
  sensibility 
  of 
  140 
  mm. 
  per 
  

   volt 
  with 
  84 
  volts 
  on 
  the 
  needle. 
  

  

  In 
  most 
  of 
  the 
  experiments 
  a 
  potentiometer 
  arrangement 
  

   was 
  employed 
  so 
  that 
  the 
  reading 
  of 
  the 
  ionization 
  current 
  

   might 
  be 
  made 
  with 
  the 
  zero 
  of 
  the 
  instrument 
  at 
  the 
  centre 
  

   of 
  the 
  swing. 
  It 
  was 
  found 
  that 
  this 
  method 
  gave 
  very 
  

   consistent 
  and 
  accurate 
  readings, 
  which 
  was 
  of 
  especial 
  

   importance 
  when 
  small 
  potentials 
  were 
  employed. 
  

  

  The 
  whole 
  apparatus 
  could 
  be 
  rendered 
  gas-tight 
  by 
  the 
  

   use 
  of 
  a 
  heavy 
  stop-cock 
  grease. 
  

  

  Experimental 
  Results. 
  

  

  4. 
  In 
  the 
  first 
  set 
  of 
  observations 
  a 
  fine 
  slit 
  5 
  mm. 
  long 
  and 
  

   0*5 
  mm. 
  in 
  width 
  was 
  placed 
  1 
  cm. 
  above 
  the 
  surface 
  of 
  the 
  

   polonium. 
  A 
  " 
  Bragg 
  " 
  curve 
  was 
  determined 
  in 
  the 
  usual 
  

   manner 
  by 
  varying 
  the 
  distance 
  of 
  the 
  polonium 
  from 
  the 
  

   electrodes. 
  The 
  range 
  of 
  the 
  alpha 
  particle 
  in 
  air 
  at 
  one 
  atmo- 
  

   sphere 
  or 
  a 
  pressure 
  of 
  760 
  mm. 
  of 
  mercury 
  was 
  found 
  to 
  be 
  

   3'8 
  cm., 
  which 
  is 
  in 
  good 
  agreement 
  with 
  that 
  observed 
  by 
  

   Levin 
  * 
  and 
  Taylor 
  f. 
  When 
  the 
  transverse 
  field 
  was 
  

   employed 
  the 
  slit 
  was 
  so 
  orientated 
  that 
  its 
  length 
  was 
  

   parallel 
  to 
  the 
  electrodes. 
  It 
  was 
  calculated 
  that 
  the 
  cone 
  

   of 
  rays 
  emerging 
  from 
  the 
  slit 
  would 
  fall 
  entirely 
  within 
  the 
  

   electrodes 
  and 
  that 
  no 
  alpha 
  particle 
  could 
  reach 
  an 
  electrode 
  

   except 
  by 
  scattering. 
  

  

  The 
  values 
  obtained 
  for 
  ri 
  and 
  r 
  t 
  for 
  different 
  values 
  of 
  the 
  

   electric 
  field 
  X 
  are 
  given 
  below, 
  and 
  the 
  corresponding 
  

  

  Table 
  I. 
  

   d=2'68 
  cm. 
  ; 
  r 
  = 
  / 
  7 
  6oA'284- 
  

  

  

  Lon 
  

  

  gitudinal 
  Field. 
  

  

  Transverse 
  Field. 
  

  

  mm. 
  

  

  X 
  

  

  volts/cm. 
  

  

  _ 
  h- 
  

  

  r 
  v 
  

  

  X. 
  

  

  i 
  . 
  

   t 
  

  

  V 
  

  

  160 
  

  

  1565 
  

  

  0-65 
  

  

  

  625 
  

  

  043 
  

  

  

  284 
  

  

  1565 
  

  

  1-22 
  

  

  

  625 
  

  

  0-82 
  

  

  

  770 
  

  

  25 
  

  

  351 
  

  

  2-88 
  

  

  4 
  

  

  1-91 
  

  

  2-33 
  

  

  770 
  

  

  50 
  

  

  3-88 
  

  

  3-18 
  

  

  20 
  

  

  253 
  

  

  309 
  

  

  770 
  

  

  105 
  

  

  4-05 
  

  

  3-32 
  

  

  42 
  

  

  2-80 
  

  

  3-42 
  

  

  770 
  

  

  525 
  

  

  4-46 
  

  

  3-66 
  

  

  125 
  

  

  299 
  

  

  3-65 
  

  

  770 
  

  

  1045 
  

  

  4-53 
  

  

  371 
  

  

  210 
  

  

  2-96 
  

  

  3-62 
  

  

  770 
  

  

  1575 
  

  

  4-61 
  

  

  3-78 
  

  

  625 
  

  

  2-98 
  

  

  364 
  

  

  * 
  Levin, 
  Am. 
  J. 
  Sci. 
  [4] 
  xxii. 
  p. 
  8 
  (1906). 
  

   t 
  Taylor, 
  ibid. 
  [4] 
  xxvi. 
  p. 
  169 
  (1908). 
  

  

  