﻿574 
  

  

  Dr. 
  C. 
  G. 
  Barkla 
  and 
  Mr. 
  C. 
  A. 
  Sadler 
  

  

  The 
  evidence 
  o£ 
  polarity 
  of 
  the 
  primary 
  given 
  by 
  the 
  

   radiation 
  from 
  tin 
  disappears 
  for 
  even 
  softer 
  primary 
  rays 
  

   than 
  in 
  the 
  case 
  of 
  silver. 
  This 
  must 
  be 
  connected 
  with 
  the 
  

   fact 
  that 
  the 
  characteristic 
  homogeneous 
  radiation 
  from 
  tin 
  

   is 
  less 
  penetrating 
  than 
  that 
  from 
  silver, 
  and 
  is 
  set 
  up 
  by 
  a 
  

   less 
  penetrating 
  primary 
  radiation. 
  It 
  thus 
  appears 
  earlier 
  

   in 
  the 
  process 
  of 
  hardening 
  the 
  primary 
  and 
  swamps 
  the 
  

   effect 
  of 
  the 
  scattered 
  radiation 
  sooner. 
  

  

  Table 
  YITT. 
  

  

  I. 
  

  

  Absorption 
  

  

  of 
  Primary 
  

  

  by 
  -01 
  Al. 
  

  

  II. 
  

  

  Ratio 
  of 
  Ionizations 
  in 
  

  

  Secondary 
  and 
  Primary 
  

  

  electroscopes. 
  

  

  III. 
  

  

  Percentage 
  A 
  r 
  ariation 
  of 
  

  

  intensity 
  of 
  Secondary 
  

  

  radiation 
  exhibiting 
  polarity 
  

  

  of 
  Primary 
  beam. 
  

  

  

  O 
  radiator. 
  Ag 
  radiator. 
  

  

  C 
  radiator. 
  

  

  Ag 
  radiator. 
  

  

  35-5 
  

  

  •303 
  -180 
  

  

  14 
  

  

  11-5 
  

  

  32-6 
  

  

  •340 
  

  

  •350 
  

  

  1095 
  

  

  4-45 
  

  

  32-3 
  

  

  •318 
  -305 
  

  

  12-9 
  

  

  0-2 
  

  

  £2-0 
  

  

  •315 
  -360 
  

  

  129 
  

  

  4-5 
  

  

  30 
  

  

  •349 
  

  

  •821 
  

  

  9-9 
  

  

  2-8 
  

  

  20-4 
  

  

  •353 
  

  

  •844 
  

  

  96 
  

  

  2-45 
  

  

  28-0 
  

  

  •364 
  

  

  1-12 
  

  

  915 
  

  

  •9 
  

  

  28-0 
  

  

  •380 
  

  

  1-35 
  

  

  7-5 
  

  

  •75 
  

  

  273 
  

  

  •405 
  

  

  1-G2 
  

  

  7 
  

  

  •45 
  

  

  256 
  

  

  •425 
  

  

  1-82 
  

  

  6'5 
  

  

  

  

  Homogeneous 
  Rays. 
  — 
  An 
  analysis 
  of 
  the 
  radiation 
  from 
  

   silver 
  similar 
  to 
  that 
  made 
  of 
  the 
  radiation 
  from 
  elements 
  of 
  

   the 
  Cr-Zn 
  group 
  shows 
  that 
  when 
  the 
  primary 
  radiation 
  is 
  

   moderately 
  penetrating, 
  such 
  a 
  homogeneous 
  secondary 
  radia- 
  

   tion 
  constitutes 
  the 
  bulk 
  of 
  the 
  rays 
  emitted. 
  Absorption 
  

   by 
  thin 
  sheets 
  of 
  aluminium 
  showed 
  slight 
  heterogeneity 
  at 
  

   first, 
  such 
  as 
  would 
  be 
  evident 
  if 
  the 
  scattered 
  radiation 
  were 
  

   superposed 
  on 
  the 
  more 
  penetrating 
  homogeneous 
  radiation. 
  

   After 
  the 
  absorption 
  of 
  this 
  more 
  easily 
  absorbed 
  scattered 
  

   radiation 
  the 
  remainder 
  appeared 
  perfectly 
  homogeneous. 
  

  

  The 
  contrast 
  between 
  the 
  constitution 
  of 
  the 
  copper 
  and 
  

   silver 
  radiations 
  is 
  shown 
  by 
  the 
  curves 
  given 
  in 
  fig. 
  1. 
  In 
  

   the 
  copper 
  radiation 
  the 
  homogeneous 
  rays 
  are 
  more 
  easily 
  

   absorbed 
  than 
  the 
  scattered 
  rays, 
  so 
  the 
  curve 
  is 
  initially 
  

   horizontal 
  and 
  finally 
  slopes 
  downwards. 
  In 
  the 
  silver 
  

   radiation 
  the 
  scattered 
  rays 
  are 
  on 
  the 
  average 
  more 
  easily 
  

  

  