﻿774 
  Dr. 
  Norman 
  Campbell 
  on 
  the 
  

  

  during 
  the 
  periods 
  elapsing 
  between 
  the 
  carrying 
  out 
  of 
  the 
  

   three 
  experiments, 
  it 
  is 
  doubtful 
  whether 
  the 
  magnetometer 
  

   method 
  can 
  be 
  relied 
  on 
  to 
  the 
  fourth 
  figure. 
  

  

  The 
  solenoid 
  method 
  seems 
  to 
  be 
  reliable, 
  accurate, 
  and 
  

   easily 
  carried 
  out. 
  Although 
  the 
  preliminary 
  parts 
  of 
  the 
  

   above 
  investigation 
  were 
  rather 
  lengthy, 
  little 
  difficulty 
  was 
  

   experienced 
  once 
  the 
  actual 
  form 
  of 
  the 
  different 
  parts 
  of 
  

   the 
  apparatus 
  had 
  been 
  decided 
  upon. 
  In 
  any 
  future 
  ex- 
  

   periments 
  with 
  the 
  same 
  apparatus 
  none 
  of 
  the 
  preliminary 
  

   experiments 
  will 
  have 
  to 
  be 
  performed, 
  and 
  the 
  whole 
  of 
  the 
  

   observations 
  could 
  be 
  made 
  within 
  one 
  hour. 
  

  

  If 
  the 
  apparatus 
  were 
  fitted 
  up 
  in 
  a 
  permanent 
  magnetic 
  

   laboratory 
  the 
  helix 
  might 
  be 
  made 
  of 
  considerable 
  size, 
  or 
  

   even 
  replaced 
  by 
  a 
  prolate 
  spheroid 
  with 
  windings 
  at 
  equal 
  

   latitude 
  distances. 
  This 
  would 
  eliminate 
  the 
  difficulty 
  of 
  

   obtaining 
  a 
  very 
  accurate 
  value 
  for 
  the 
  period 
  of 
  oscillation, 
  

   as 
  the 
  suspension 
  fibre 
  could 
  be 
  made 
  longer 
  in 
  a 
  larger 
  

   apparatus. 
  

  

  The 
  instrument 
  can 
  be 
  adapted 
  to 
  measure 
  declination, 
  

   and 
  has 
  been 
  successfully 
  used 
  for 
  that 
  purpose, 
  but 
  the 
  

   method 
  was 
  rather 
  laborious. 
  

  

  In 
  conclusion 
  I 
  wish 
  to 
  thank 
  Mr. 
  Southern 
  for 
  his 
  check 
  

   experiment 
  with 
  the 
  Kew 
  magnetometer, 
  and 
  to 
  express 
  my 
  

   great 
  indebtedness 
  to 
  Dr. 
  Hicks 
  — 
  to 
  whose 
  suggestion 
  the 
  

   experiment 
  was 
  due 
  — 
  for 
  his 
  many 
  valuable 
  suggestions 
  and 
  

   kind 
  interest 
  in 
  the 
  work. 
  

  

  Cavendish 
  Laboratory, 
  Cambridge, 
  

   May 
  23, 
  1913. 
  

  

  LXIY. 
  Note 
  on 
  the 
  Velocity 
  of 
  8 
  Rays. 
  

   By 
  Norman 
  Campbell, 
  Sc.D.* 
  

  

  IN 
  a 
  recent 
  paper 
  (Phil. 
  Mag. 
  June 
  1913, 
  p. 
  804) 
  an 
  

   attempt 
  was 
  made 
  to 
  explain 
  on 
  the 
  basis 
  of 
  J. 
  J. 
  

   Thomson's 
  theory 
  of 
  ionization 
  by 
  charged 
  particles 
  the 
  

   observed 
  distribution 
  of 
  velocities 
  among 
  8 
  rays 
  from 
  metals. 
  

   It 
  was 
  shown 
  that 
  that 
  theory 
  predicted 
  that 
  the 
  distribution 
  

   should 
  be 
  independent 
  of 
  the 
  nature 
  of 
  the 
  primary 
  rays, 
  

   but 
  that 
  it 
  gave 
  too 
  small 
  a 
  value 
  for 
  the 
  number 
  of 
  Yerj 
  

   vslow 
  & 
  rays 
  (under 
  20 
  volts). 
  This 
  discrepancy 
  is 
  removed 
  

   by 
  the 
  recent 
  work 
  of 
  Bumstead 
  (Phil. 
  Mag. 
  Aug. 
  1913, 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  