﻿51Jr 
  Prof. 
  Wellisch 
  and 
  Dr. 
  Woodrow 
  : 
  Experiments 
  

  

  previously 
  been 
  employed 
  by 
  Wheelock 
  * 
  in 
  his 
  experiments 
  

   on 
  alpha-ray 
  ionization. 
  A 
  general 
  idea 
  of 
  the 
  apparatus 
  

   and 
  the 
  general 
  scheme 
  of 
  connexions 
  may 
  be 
  obtained 
  from 
  

   fio-. 
  1. 
  For 
  the 
  vertical 
  longitudinal 
  field 
  the 
  ionization 
  

   vessel 
  consisted 
  of 
  a 
  wire 
  gauze 
  B, 
  7*5 
  cm. 
  in 
  diameter, 
  

   situated 
  4 
  mm. 
  below 
  a 
  circular 
  brass 
  plate 
  A, 
  which 
  was 
  

   connected 
  to 
  one 
  pair 
  of 
  quadrants 
  of 
  a 
  Dolezalek 
  electro- 
  

   meter. 
  The 
  lower 
  gauze 
  G 
  was 
  inserted 
  as 
  usual, 
  to 
  avoid 
  

   disturbances 
  due 
  to 
  diffusion 
  of 
  ions 
  into 
  the 
  region 
  AB. 
  

  

  For 
  the 
  horizontal 
  transverse 
  field 
  two 
  brass 
  plates 
  were 
  

   employed, 
  one 
  C 
  (8*5 
  x 
  2*5 
  cm.) 
  connected 
  to 
  the 
  battery, 
  

   and 
  the 
  other 
  D 
  (7*2 
  X 
  0*4 
  cm.), 
  which 
  connected 
  with 
  the 
  

   electrometer. 
  The 
  latter 
  electrode 
  was 
  surrounded 
  by 
  an 
  

   earthed 
  plate 
  E, 
  which 
  served 
  as 
  a 
  guard 
  ring. 
  

  

  Both 
  the 
  longitudinal 
  and 
  the 
  transverse 
  fields 
  were 
  so 
  

   constructed 
  that 
  they 
  could 
  be 
  inserted 
  in 
  the 
  same 
  containing 
  

   Tsssel 
  as 
  shown 
  in 
  the 
  diagram. 
  

  

  A 
  thin 
  film 
  of 
  polonium 
  deposited 
  on 
  a 
  copper 
  plug, 
  

   4 
  mm. 
  in 
  diameter, 
  which 
  had 
  been 
  prepared 
  previously 
  by 
  

   Prof. 
  Boltwood, 
  was 
  employed 
  as 
  the 
  alpha-ray 
  source. 
  

   This 
  plug 
  was 
  placed 
  on 
  the 
  carrier 
  It, 
  which 
  could 
  be 
  moved 
  

   vertically 
  by 
  a 
  screw, 
  S. 
  A 
  scale 
  and 
  divided 
  head 
  enabled 
  

   one 
  to 
  make 
  a 
  very 
  accurate 
  determination 
  of 
  the 
  distance 
  

   of 
  the 
  polonium 
  from 
  the 
  centre 
  of 
  the 
  ionization 
  vessel. 
  

   A 
  narrow 
  beam 
  of 
  alpha 
  rays 
  was 
  always 
  employed 
  ; 
  this 
  

   was 
  obtained 
  by 
  placing 
  over 
  the 
  polonium 
  a 
  fine 
  slit 
  or 
  

   a 
  series 
  of 
  fine 
  " 
  canals 
  " 
  as 
  described 
  below. 
  

  

  * 
  Wheelock, 
  Am. 
  J. 
  Sci. 
  [4] 
  xxx. 
  p. 
  233 
  (1910). 
  

  

  