﻿Radioactivity 
  imparted 
  to 
  Salts 
  by 
  Cathode 
  Rays. 
  195 
  

  

  It 
  is 
  perhaps 
  worth 
  noticing 
  that 
  if 
  the 
  dotted 
  part 
  of 
  the 
  

   Fe-Cu 
  curve 
  (fig. 
  5) 
  (which 
  is 
  marked 
  HI 
  and 
  represents 
  

   the 
  first 
  few 
  points 
  obtained 
  by 
  heating 
  a 
  fresh 
  couple 
  in 
  

   hydrogen) 
  be 
  produced, 
  it 
  cuts 
  the 
  upper 
  and 
  " 
  constant" 
  

   portion 
  of 
  the 
  curve 
  at 
  a 
  temperature 
  just 
  below 
  800°, 
  the 
  

   temperature 
  of 
  the 
  resistance-changes 
  in 
  iron. 
  

  

  In 
  conclusion 
  I 
  wish 
  to 
  express 
  my 
  best 
  thanks 
  to 
  Professor 
  

   Callendar, 
  F.R.S., 
  for 
  constant 
  help 
  and 
  advice 
  during 
  this 
  

   research, 
  which 
  was 
  undertaken 
  at 
  his 
  suggestion. 
  

  

  My 
  thanks 
  are 
  also 
  due 
  to 
  Mr. 
  G. 
  M. 
  Gibbins, 
  of 
  University 
  

   College, 
  for 
  help 
  during 
  the 
  first 
  part 
  of 
  the 
  thermoelectric 
  

   measurements. 
  

  

  XX. 
  On 
  a 
  kind 
  of 
  Radioactivity 
  imparted 
  to 
  certain 
  Salts 
  

   by 
  Cathode 
  Rays. 
  By 
  J. 
  C. 
  McLennan, 
  Ph.D., 
  Demon- 
  

   strator 
  in 
  Physics, 
  University 
  of 
  Toronto*. 
  

  

  i 
  

  

  I. 
  Introduction. 
  

  

  T 
  has 
  been 
  shown 
  by 
  Curie 
  f 
  that 
  every 
  substance, 
  placed 
  

   in 
  the 
  neighbourhood 
  of 
  radium, 
  itself 
  acquires 
  a 
  radio- 
  

   activity 
  which 
  persists 
  for 
  many 
  hours 
  and 
  even 
  days 
  after 
  

   the 
  removal 
  of 
  the 
  radium. 
  Curie 
  % 
  has 
  also 
  obtained 
  a 
  

   similar 
  but 
  more 
  feeble 
  effect 
  with 
  the 
  active 
  preparation 
  

   polonium. 
  

  

  Rutherford 
  §, 
  too, 
  has 
  shown 
  that 
  thorium 
  compounds 
  

   under 
  certain 
  conditions 
  possess 
  the 
  property 
  of 
  producing 
  

   temporary 
  radioactivity 
  in 
  all 
  solid 
  substances 
  in 
  their 
  

   neighbourhood. 
  

  

  Up 
  to 
  the 
  present 
  time 
  we 
  appear 
  to 
  have 
  only 
  two 
  recorded 
  

   cases 
  of 
  substances 
  becoming 
  radioactive 
  by 
  the 
  action 
  of 
  

   cathode 
  rays. 
  

  

  Hofmann 
  and 
  Strauss 
  || 
  observed 
  that 
  radioactive 
  lead 
  

   sulphate 
  prepared 
  from 
  the 
  minerals 
  uranpecherz, 
  broggerite, 
  

   cleveite, 
  uranglimmer, 
  and 
  samarskite, 
  after 
  losing 
  its 
  activity 
  

   through 
  lapse 
  of 
  time, 
  was 
  again 
  made 
  radioactive 
  by 
  exposing 
  

   it 
  to 
  cathode 
  rays. 
  

  

  Villard 
  H 
  found 
  that 
  a 
  small 
  piece 
  of 
  bismuth 
  which 
  had 
  

   been 
  used 
  as 
  the 
  anticathode 
  of 
  a 
  discharge-tube 
  produced 
  a 
  

  

  * 
  Communicated 
  by 
  Prof. 
  J. 
  J. 
  Thomson. 
  

  

  t 
  Rapports 
  presentes 
  au 
  Congres 
  International 
  de 
  Physique, 
  Paris, 
  

   tome 
  iii. 
  p. 
  108 
  (1900). 
  

  

  t 
  Curie, 
  Comptes 
  Rendus, 
  t. 
  cxxix. 
  p. 
  714, 
  Nov. 
  1899. 
  

  

  § 
  Eutherford, 
  Phil. 
  Mag. 
  vol. 
  xlix. 
  p. 
  161 
  (1900). 
  

  

  || 
  Chem. 
  Ber. 
  xxxiv. 
  pp. 
  8-11 
  & 
  907-13; 
  Beibl. 
  xxv. 
  pp. 
  317 
  & 
  633 
  

   (1901). 
  ; 
  

  

  % 
  Villard, 
  Societe 
  de 
  Physique, 
  juillet 
  1900. 
  

  

  02 
  

  

  