﻿imparted 
  to 
  certain 
  Salts 
  by 
  Cathode 
  Rays. 
  201 
  

  

  when 
  heated 
  without 
  being 
  previously 
  exposed 
  to 
  cathode 
  

   rays 
  or 
  to 
  the 
  spark-discharge. 
  

  

  As 
  an 
  example 
  of 
  the 
  magnitude 
  of 
  the 
  effects 
  described 
  

   in 
  this 
  paper, 
  it 
  may 
  be 
  stated 
  that 
  in 
  one 
  instance 
  the 
  

   radiation 
  from 
  a 
  thin 
  layer 
  of 
  active 
  calcium 
  sulphate, 
  spread 
  

   on 
  the 
  base 
  of 
  the 
  electroscope 
  over 
  an 
  area 
  of 
  twenty 
  

   square 
  centimetres, 
  discharged 
  from 
  two 
  to 
  three 
  electro- 
  

   static 
  units 
  of 
  positive 
  electricity. 
  

  

  V. 
  Impressed 
  Radioactivity 
  and 
  Thermoluminescence. 
  

  

  E. 
  Wiedemann 
  * 
  has 
  shown 
  that 
  a 
  number 
  of 
  substances, 
  

   when 
  exposed 
  to 
  cathode 
  rays 
  or 
  to 
  the 
  spark-discharge, 
  

   acquire 
  and 
  possess 
  for 
  some 
  time 
  the 
  power 
  of 
  becoming 
  

   luminous 
  when 
  their 
  temperature 
  is 
  raised 
  to 
  a 
  point 
  far 
  

   below 
  that 
  at 
  which 
  they 
  become 
  luminous 
  in 
  their 
  normal 
  

   state. 
  To 
  this 
  phenomenon 
  he 
  has 
  given 
  the 
  name 
  thermo- 
  

   luminescence. 
  

  

  Now 
  the 
  methods 
  of 
  exciting 
  this 
  phenomenon 
  are 
  pre- 
  

   cisely 
  the 
  same 
  as 
  those 
  adopted 
  in 
  imparting 
  radioactivity 
  to 
  

   the 
  various 
  salts 
  just 
  mentioned 
  ; 
  and 
  as 
  the 
  range 
  of 
  tempera- 
  

   tures 
  over 
  which 
  both 
  phenomena 
  appear 
  is 
  about 
  the 
  same, 
  it 
  

   seemed 
  possible 
  that 
  some 
  connexion 
  might 
  exist 
  between 
  the 
  

   two 
  effects. 
  

  

  To 
  investigate 
  this 
  point 
  each 
  of 
  the 
  salts 
  was 
  carefully 
  

   tested 
  for 
  thermoluminescence, 
  and 
  the 
  results 
  obtained 
  are 
  

   recorded 
  in 
  column 
  III., 
  Table 
  I. 
  A 
  reference 
  to 
  this 
  table 
  

   will 
  show 
  that 
  in 
  the 
  case 
  of 
  three 
  salts 
  only 
  was 
  the 
  radio- 
  

   activity 
  accompanied 
  by 
  the 
  phenomenon 
  of 
  thermolumines- 
  

   cence. 
  In 
  the 
  case 
  of 
  the 
  remaining 
  salts, 
  some 
  exhibited 
  

   thermoluminescence, 
  but 
  not 
  radioactivity, 
  while 
  with 
  others 
  

   radioactivitv 
  was 
  observed, 
  but 
  no 
  visible 
  thermoluminescence. 
  

  

  From 
  these 
  results 
  it 
  seemed 
  clear 
  that 
  no 
  connexion 
  

   existed 
  between 
  the 
  two 
  phenomena 
  ; 
  but 
  in 
  order 
  to 
  test 
  

   the 
  matter 
  still 
  further, 
  some 
  experiments 
  were 
  made 
  with 
  a 
  

   number 
  of 
  Van'tHofFsf 
  so-called 
  solid 
  solutions, 
  which 
  were 
  

   known 
  to 
  exhibit 
  a 
  powerful 
  thermoluminescence. 
  From 
  

   Table 
  II., 
  which 
  contains 
  a 
  summary 
  of 
  the 
  results, 
  it 
  will 
  

   be 
  seen 
  that 
  radioactivity 
  was 
  observed 
  with 
  but 
  one 
  solution, 
  

   namely 
  CaS0 
  4 
  + 
  2 
  p.c. 
  MnS0 
  4 
  . 
  The 
  radioactivity 
  obtained 
  

   in 
  this 
  case 
  was 
  practically 
  of 
  the 
  same 
  intensity 
  as 
  that 
  

   obtained 
  with 
  the 
  simple 
  salt, 
  calcium 
  sulphate. 
  

  

  * 
  Zeitschr.f. 
  Electrochem. 
  vol. 
  ii. 
  p. 
  159 
  (1895). 
  

   + 
  Zeitschriftf.phya. 
  Chemie, 
  vol. 
  v. 
  p. 
  322 
  (1890). 
  

  

  