﻿752 
  Mr. 
  W. 
  A. 
  Jenkins: 
  New 
  Method 
  of 
  Determining 
  the 
  

  

  obtained 
  for 
  " 
  q-" 
  by 
  Simpson 
  and 
  Wright 
  with 
  a 
  zinc 
  

   receiver 
  of 
  about 
  27 
  litres 
  capacity, 
  and 
  a 
  value 
  of 
  4 
  ions 
  

   per 
  c.c. 
  per 
  sec. 
  by 
  the 
  writers 
  with 
  an 
  ionization-chamber 
  of 
  

   the 
  same 
  metal 
  of 
  only 
  2 
  litres 
  capacity, 
  one 
  is 
  led 
  to 
  the 
  

   conclusion 
  that 
  the 
  experimental 
  results 
  obtained 
  so 
  far 
  lend 
  

   no 
  support 
  to 
  the 
  view 
  that 
  the 
  residual 
  ionization 
  obtained 
  

   in 
  air 
  confined 
  in 
  zinc 
  receivers 
  is 
  due 
  to 
  a 
  radiation 
  emitted 
  

   by 
  the 
  walls. 
  It 
  would 
  be 
  interesting, 
  however, 
  to 
  see 
  what 
  

   resulted 
  if 
  receivers 
  of 
  still 
  smaller 
  capacity 
  than 
  two 
  litres 
  

   were 
  used. 
  On 
  the 
  other 
  hand, 
  it 
  has 
  been 
  shown 
  by 
  J. 
  J. 
  

   Thomson 
  *, 
  and 
  again 
  recently 
  by 
  Langevin 
  and 
  J. 
  J. 
  Rey 
  f, 
  

   that 
  one 
  cannot 
  account 
  for 
  this 
  residual 
  ionization 
  by 
  sup- 
  

   posing 
  it 
  due 
  to 
  collisions 
  between 
  the 
  molecules, 
  for, 
  on 
  this 
  

   hypothesis, 
  the 
  increase 
  in 
  ionization 
  with 
  a 
  rise 
  in 
  tempera- 
  

   ture 
  should 
  be 
  enormously 
  greater 
  than 
  any 
  increase 
  which 
  

   has 
  been 
  observed. 
  

  

  The 
  writers 
  wish 
  to 
  acknowledge 
  their 
  indebtedness 
  to 
  

   Messrs. 
  P. 
  Blackman, 
  G. 
  S. 
  Campbell, 
  and 
  E. 
  C. 
  Henderson 
  

   for 
  their 
  kindness 
  in 
  making 
  corroborative 
  measurements 
  at 
  

   various 
  times 
  during 
  the 
  investigation. 
  

  

  The 
  Physical 
  Laboratory, 
  

   The 
  University 
  of 
  Toronto, 
  

   July 
  1st, 
  1913. 
  

  

  LXIII. 
  On 
  a 
  New 
  Method 
  of 
  Determining 
  the 
  Horizontal 
  

   Intensity 
  of 
  the 
  Earth's 
  Magnetic 
  Field. 
  By 
  Walter 
  A. 
  

   Jenkins, 
  M.Sc. 
  (1851 
  Exhibitioner) 
  %. 
  

  

  THE 
  ordinary 
  method 
  for 
  the 
  determination 
  of 
  the 
  

   horizontal 
  component 
  of 
  the 
  earth's 
  magnetic 
  field 
  

   is 
  somewhat 
  lengthy 
  and 
  involves 
  several 
  troublesome 
  

   corrections. 
  The 
  following 
  method, 
  while 
  as 
  accurate 
  as 
  the 
  

   old 
  one, 
  possesses 
  the 
  very 
  great 
  advantage 
  of 
  involving 
  no 
  

   corrections. 
  

  

  The 
  principle 
  of 
  the 
  method 
  is 
  the 
  production 
  of 
  a 
  known 
  

   field 
  opposite 
  to 
  that 
  of 
  the 
  earth's 
  and 
  twice 
  its 
  magnitude. 
  

   The 
  equality 
  of 
  the 
  two 
  fields 
  — 
  that 
  due 
  to 
  the 
  earth 
  and 
  that 
  

   due 
  to 
  the 
  combination 
  of 
  the 
  earth's 
  and 
  the 
  produced 
  

   one 
  — 
  is 
  determined 
  by 
  the 
  equality 
  of 
  the 
  times 
  of 
  vibration 
  

   of 
  the 
  same 
  magnet, 
  when 
  the 
  applied 
  field 
  is 
  off 
  and 
  on, 
  and 
  

   the 
  applied 
  field 
  is 
  determined 
  by 
  measuring 
  the 
  current 
  

   producing 
  it. 
  

  

  * 
  J. 
  J. 
  Thomson, 
  ' 
  Conduction 
  of 
  Electricity 
  through 
  Gases/ 
  2nd 
  ed., 
  

   p. 
  294. 
  

  

  t 
  Langevin 
  & 
  J. 
  J. 
  Rey, 
  Le 
  Radium, 
  April 
  1913, 
  p. 
  139. 
  

   X 
  Communicated 
  by 
  Prof. 
  W. 
  M. 
  Hicks, 
  F.R.S. 
  

  

  