﻿Scattering 
  and 
  Absorption 
  of 
  the 
  y 
  Rays 
  of 
  Radium. 
  611 
  

  

  (iii.) 
  Owing 
  to 
  difficulties 
  attending 
  measurements 
  from 
  

   structures 
  or 
  from 
  balloons 
  it 
  might 
  be 
  advantageous 
  to 
  keep 
  

   the 
  electroscope 
  at 
  various 
  heights 
  by 
  means 
  of 
  a 
  small 
  pilot 
  

   balloon 
  capable 
  of 
  being 
  reeled 
  in 
  so 
  quickly 
  that 
  the 
  rate 
  

   of 
  leak 
  during 
  ascent 
  or 
  descent 
  may 
  be 
  neglected 
  or, 
  at 
  

   any 
  rate, 
  allowed 
  for 
  : 
  active 
  deposit 
  at 
  various 
  heights 
  

   should 
  be 
  tested 
  for 
  by 
  means 
  of 
  a 
  dummy 
  electroscope 
  

   similarly 
  exposed 
  and 
  a 
  correction 
  made 
  if 
  possible. 
  At 
  the 
  

   time 
  of 
  the 
  observation 
  measurements 
  of 
  the 
  electrostatic 
  

   potential 
  gradient 
  should 
  be 
  made 
  and 
  a 
  record 
  kept 
  of 
  other 
  

   meteorological 
  conditions. 
  

  

  McGill 
  University, 
  Montreal, 
  

   July 
  10th, 
  i913. 
  

  

  LI. 
  The 
  Scattering 
  and 
  Absorption 
  of 
  the 
  y 
  Rays 
  of 
  Radium. 
  

   By 
  J. 
  A. 
  Gray, 
  1).Sc* 
  

  

  IT 
  was 
  discovered 
  by 
  Evef 
  that 
  secondary 
  7 
  rays 
  were 
  

   emitted 
  by 
  any 
  body 
  or 
  radiator 
  through 
  which 
  the 
  

   7 
  rays 
  of 
  radium 
  passed, 
  the 
  secondary 
  rays 
  being 
  less 
  

   penetrating 
  than 
  the 
  primary 
  rays 
  J. 
  Investigations 
  on 
  the 
  

   nature 
  of 
  these 
  secondary 
  rays 
  have 
  since 
  been 
  carried 
  out 
  

   by 
  Kleeman§, 
  Madsen 
  ||, 
  and 
  Florance 
  H, 
  the 
  experiments 
  of 
  

   Florance 
  giving 
  us 
  perhaps 
  the 
  most 
  definite 
  information. 
  

   Florance 
  ascribed 
  the 
  secondary 
  7 
  rays 
  to 
  scattering 
  of 
  the 
  

   primary 
  rays, 
  as 
  the 
  quality 
  of 
  the 
  secondary 
  rays 
  appeared 
  

   to 
  be 
  independent 
  of 
  the 
  nature 
  of 
  the 
  radiator. 
  He 
  obtained 
  

   the 
  important 
  result 
  that 
  the 
  secondary 
  or 
  scattered 
  rays 
  

   became 
  less 
  penetrating 
  as 
  the 
  angle 
  of 
  scattering 
  increased. 
  

   It 
  appeared 
  as 
  if 
  much 
  more 
  7 
  radiation 
  was 
  scattered 
  in 
  

   the 
  emergent 
  direction 
  than 
  in 
  the 
  incident 
  direction, 
  the 
  

   scattering 
  being 
  apparently 
  similar 
  to 
  that 
  suffered 
  by 
  a 
  

   pencil 
  of 
  a 
  or 
  /3 
  rays. 
  As 
  the 
  primary 
  rays 
  were 
  hetero- 
  

   geneous, 
  Florance 
  explained 
  his 
  results 
  by 
  assuming 
  that 
  

   the 
  softer 
  rays 
  were 
  scattered 
  through 
  larger 
  angles 
  

  

  * 
  Communicated 
  bv 
  Professor 
  H. 
  T. 
  Barnes, 
  F.R.S. 
  

  

  t 
  Eve, 
  Phil. 
  Mag. 
  viii. 
  p. 
  669 
  (1904). 
  

  

  % 
  In 
  this 
  paper 
  y 
  rays 
  striking 
  a 
  body 
  or 
  radiator 
  are 
  referred 
  to 
  as 
  

   primary 
  rays, 
  rays 
  coming 
  off 
  from 
  the 
  radiator 
  in 
  a 
  different 
  direction 
  

   as 
  secondary 
  rays. 
  The 
  secondary 
  rays 
  are 
  ascribed 
  to 
  scattering, 
  and 
  

   the 
  angle 
  between 
  the 
  direction 
  of 
  these 
  rays 
  and 
  that 
  of 
  the 
  primary 
  is 
  

   called 
  the 
  angle 
  of 
  scattering. 
  

  

  § 
  Kleeman, 
  Phil. 
  Mag. 
  xv. 
  p. 
  638 
  (1908). 
  

  

  || 
  Madsen, 
  Phil. 
  Mag. 
  xvii. 
  p. 
  423 
  (1909). 
  

  

  % 
  Florance, 
  Phil. 
  Mag. 
  xx. 
  p. 
  921 
  (1910). 
  

  

  