﻿436 
  Mr. 
  C. 
  A. 
  Chant 
  : 
  An 
  Experimental 
  Investigation 
  

  

  when 
  the 
  detector, 
  fully 
  saturated, 
  was 
  pushed 
  into 
  the 
  tube 
  

   T, 
  the 
  magnetometer 
  deflexion 
  was 
  40 
  cms., 
  the 
  scale 
  being 
  

   numbered 
  so 
  that 
  this 
  read 
  zero. 
  After 
  partial 
  demagnetiza- 
  

   tion 
  through 
  the 
  electrical 
  oscillations, 
  it 
  was 
  replaced 
  in 
  its 
  

   position 
  behind 
  the 
  magnetometer 
  and 
  the 
  alteration 
  in 
  

   reading 
  observed 
  directly. 
  

  

  It 
  was 
  found 
  that 
  the 
  detector 
  could 
  be 
  removed 
  and 
  

   replaced 
  with 
  no 
  observable 
  difference 
  in 
  the 
  reading 
  ; 
  and 
  

   successive 
  magnetizations 
  to 
  saturation 
  produced 
  the 
  same 
  

   deflexion. 
  

  

  Rutherford* 
  showed 
  that 
  the 
  demagnetization 
  produced 
  

   by 
  rapid 
  oscillations 
  is 
  confined 
  to 
  the 
  outer 
  layers 
  of 
  the 
  

   magnet. 
  The 
  diffusion 
  of 
  the 
  magnetic 
  force 
  from 
  the 
  

   dielectric 
  into 
  a 
  magnetizable 
  substance 
  is, 
  indeed, 
  similar 
  to 
  

   the 
  passage 
  of 
  electrical 
  action 
  into 
  a 
  conductor. 
  Hence 
  for 
  

   rapidly 
  alternating 
  currents 
  the 
  magnetic 
  action 
  is 
  confined 
  

   to 
  the 
  outer 
  layers, 
  the 
  more 
  rapid 
  the 
  alternation 
  the 
  thinner 
  

   the 
  layer 
  affected. 
  Hence 
  the 
  reason 
  for 
  using 
  fine 
  wire 
  and 
  

   insulating 
  the 
  pieces 
  from 
  each 
  other. 
  By 
  so 
  doing 
  more 
  

   surface 
  is 
  presented 
  to 
  the 
  dielectric 
  and 
  the 
  effect 
  is 
  greater. 
  

   In 
  some 
  of 
  his 
  detectors 
  Rutherford 
  used 
  iron 
  wire 
  0"07 
  mm. 
  

   in 
  diameter 
  (i. 
  e. 
  only 
  one 
  half 
  the 
  diameter 
  of 
  mine), 
  with 
  

   160 
  turns 
  of 
  fine 
  wire 
  on 
  the 
  helix, 
  and 
  much 
  longer 
  wings. 
  

   Thus 
  he 
  was 
  able 
  to 
  obtain 
  noticeable 
  effects 
  at 
  a 
  distance 
  of 
  

   over 
  half 
  a 
  mile 
  from 
  the 
  oscillator, 
  which 
  consisted 
  of 
  large 
  

   plates. 
  My 
  detector, 
  however, 
  was 
  sensitive 
  enough 
  for 
  my 
  

   purpose. 
  

  

  In 
  the 
  report 
  f 
  on 
  Hertzian 
  Oscillations 
  which 
  Righi 
  pre- 
  

   sented 
  to 
  the 
  International 
  Congress 
  of 
  Physicists 
  in 
  Paris 
  in 
  

   1900, 
  he 
  enumerated 
  21 
  kinds 
  of 
  apparatus 
  for 
  indicating 
  

   the 
  presence 
  of 
  electric 
  oscillations. 
  Of 
  these 
  the 
  magnetic 
  

   detector 
  is 
  one 
  of 
  the 
  easiest 
  to 
  manage 
  and 
  possibly 
  the 
  

   simplest 
  for 
  quantitative 
  comparisons, 
  though 
  I 
  know 
  of 
  few 
  

   investigations 
  in 
  which 
  it 
  has 
  been 
  used 
  J. 
  Its 
  sensitiveness 
  

   increases 
  as 
  the 
  wings 
  are 
  lengthened, 
  and 
  the 
  greatest 
  

   difficulty 
  I 
  experienced 
  arose 
  from 
  the 
  fact 
  that 
  it 
  is 
  specially 
  

   sensitive 
  to 
  the 
  surgings 
  in 
  the 
  connecting 
  wires 
  of 
  the 
  

   oscillator. 
  An 
  illustration 
  may 
  be 
  interesting. 
  

  

  A 
  wire 
  o 
  metres 
  long 
  was 
  stretched 
  from 
  one 
  terminal 
  of 
  

  

  * 
  Loc. 
  bit. 
  

  

  t 
  Rapports 
  presentes 
  an 
  Congres 
  International 
  de 
  Physique 
  reuni 
  a 
  Paris 
  

   en 
  1900, 
  Tome 
  ii. 
  p. 
  301. 
  (Paris, 
  1900.) 
  

  

  \ 
  In 
  the 
  June 
  (1901) 
  Phil. 
  Mag-, 
  is 
  a 
  paper 
  by 
  0. 
  G. 
  Barkla, 
  in 
  which 
  

   are 
  described 
  experiments 
  on 
  the 
  relative 
  velocities 
  of 
  electromagnetic 
  

   disturbances 
  along 
  wires 
  of 
  different 
  diameters, 
  in 
  which 
  the 
  magnetic 
  

   detector 
  was 
  used 
  as 
  an 
  indicator. 
  

  

  